HSCPHYSICSEM

Polarization of Light.mp4

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Tyndall Effect.mp4

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Tyndall Effect

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Effects of Radiation

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DNA Repair, Damage, Genes, Genetics

2011-10-22T23:12:00.001-07:00

How Radiation Affects DNA

2011-10-22T23:11:00.001-07:00

Cell Phone Exposure Effects on Brain; New Study Shows Impact of Radiation

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Health Effects of Electromagnetic Radiation

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How to remember the ElectroMagnetic Spectrum...

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Electromagnetic waves

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Electromagnetic wave HD

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working of laser

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Laser Helium-Neon 1mW

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How a Ruby Laser Works

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Origin of Earth's Magnetic Field

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Physics - Electromagnetism: Faraday's Law

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Electromagnetic Induction

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1940 X Ray Physics Documentary By William D Coolidge

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X RAY PHYSICS

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How X Ray Cathode Tubes Work

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Xray tube operation

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Cathode Ray Tube 2

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Millikan Oil Drop Experiment

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Ruther's Alpha Scattering Experiment2

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Cathode ray tube and electron

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J. J. Thomson ATOM MODEL

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CATHODE RAY TUBE

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TN PLUS TWO MARCH 2011 KEY ANSWERS

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TN PLUS TWO MARCH 2011 KEY ANSWERS

http://www.smartclass.kalvisolai.com/

Transformer Animation

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Transformer

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Force on a Current Carrying Conduct kept in a Magnetic Field

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D.C.MOTOR

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Applications of Eddy currents

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Eddy currents demo

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The Visible Spectrum

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The Visible Spectrum

Electromagnetic wave HD

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Electromagnetic wave HD

Charged particle in a magnetic field

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Charged particle in a magnetic field

Magnetic field in a solenoid

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Magnetic field in a solenoid

Eddy Currents and Lenz's Law

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LENZ'S LAW LEVITATION DEMONSTRATION

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A.C.GENERATOR ANIMATION 2

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A.C.GENERATOR ANIMATION

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IMPORTANT 10 MARK QUESTIONS FROM 1’st LESSON.

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IMPORTANT 10 MARK QUESTIONS FROM 1’st LESSON.

1.What is an electric dipole? Define an expression for the electric field due to an electric dipole at a point on its axial line.

(march06,09,june06,10,oct 10)

2. Derive an expression for the electric potential at a point due to ann electric dipole. Discuss the special cases.

(oct 06,march 08,june 08,march10)

3. Define an expression for the electric field due to an electric dipole at a point along the equatorial line. (march 07,june 09)

4.Deduce an expression for the equivalent capacitance of capacitors connected (i)in series and (ii) in parallel . (june 07,oct 07 )

5.State the principle and explain the construction and working of Van de Graff generator. (oct 08,09)

IMPORTANT 10 MARK QUESTIONS FROM 8’th LESSON.

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IMPORTANT 10 MARK QUESTIONS FROM 8’th LESSON.

1.Describe the principle and action of a Bainbridge mass spectrometer in determining the isotopic masses.

( JUNE 05,07,08,10, OCT 06,07,10, MARCH09 )

2. Explain the construction and working of a GM (Geiger – Muller )counter.

(March 07, June 09)

3.What are cosmic rays? Explain (i)Latitude effect (ii)Altitude effect of cosmic rays. (March 08,10)

4.Obtain an expression for the amount of the radioactive substance present at any moment . Obtain the relation between half life period and decay constant.(Oct 08 , 09 )

5. What is nuclear reactor?Explain the function of (i)moderator , (ii) control rods and (iii) neutron reflector. Mention the uses of nuclear reactor.

(March 06)

LESSON 8 IMPORTANT 10 MARK

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LESSON 1 IMPORTANT 10 MARK

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I MID TERM EXPECTED QUESTIONS .LESSONS 1,2,7,& 8 ( 5 MARKS)

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5 MARKS

LESSONS 1 AND 2

78. A parallel plate capacitor has plates of area 200 cm and separation between the plates is 1 m m. Calculate (i) the potential difference between the plates if 1 n C charge is given to the capacitor. (ii)With the same charge (1nC) if the plate separation is increased to 2 mm , what is the new potential difference and (iii) the electric field between the plates? (March 06)

79. Three capacitors each of capacitance 9 pF are connected in series. (i) What is the total capacitance of the combination? (ii) What is the potential difference across each capacitor if the combination is connected to 120 V supply? (June 06, Oct 06)

80. Write the properties of lines of forces. (Mar 07, Oct 07, Mar 08, 10)

81. Two capacitors of capacitances 0.5 F and 0.75 F are connected in parallel and the combination to a 110 V battery. Calculate the charge from the source and charge on each capacitor. (June 07)

82. Two positive charges of 12 C and 18 C respectively are 10 cm apart. Find the work done in bringing them 4 cm closer, so that they are 6 cm apart. (June 08)

83. Two capacitors of unknown capacitances are connected in series and parallel. If the net capacitances in the two combinations are 6 F and 25 F repectively, find their capacitances.
(Oct 08)

84. Define electric potential at a point obtain an expression for electric potential due to a point charge. (March 09)

85. The plates of a parallel plate capacitor have an area of 90 cm each and are separated by 2.5 mm. The capacitor is charged by connecting it to a 400 V supply. How much electrostatic energy is stored by the capacitor? (June 09)

86. What is electrostatic potential energy of a system of two point charges? (Oct 09)

87. Deduce an expression for the capacitance of a parallel plate capacitor. (June 10)

88. Derive an empression for the torque experienced by an electric dipole when placed in a uniform electric field. (Oct 10)

CURRENT ELECTRICITY

89. Define mobility. Establish a relation between drift velocity and current. (March 06)

90. Obtain the condition for bridge balance in Wheatstones bridge. (Mar 06, June 06, Oct 06, Mar 08, June 09, March 10)

91. State and verify Faraday’s second law of electrolysis. (June 06, March 08)

92. If two or more resistors are connected in parallel, derive an expression for the effective resistance. (Oct 06)

93. How will you compare the e.m.f.s of two cells using a potentiometer? (March 07, Oct; 10)

94. a) In the given network, calculate the effective resistance between points A & B.(March 07)

b) The effective resistances are 10 ohm, 2.4 ohm when they are connected in series and parallel respectively. What are the resistances of individual resistors?

95. Explain the working of a Leclanche cell with a diagram. (June 07)

96. State the explain Kirchhoff’s second law for electrical network. (June 07)

97. Explain the principle of a potentiometer. (Oct 07)

98. Explain the action of lead-acid accumulator. (Oct 07)

99. Explain the determination of the internal resistance of a cell using voltmeter. (June 08, Oct 09)

100. A copper wire of 10 m area of area of cross-section, carries a current of 2A. If the number of electrons per cubic metre is 8x10 calculate the current density and overage drift velocity (Given e=1.6x10 C) (march 09)

101. State Faraday’s first law of electrolysis and describe the experimental verification. (June 08, Oct 09)

102. Write any five applications of superconductors. (Oct 08, March 09)

103. Explain the construction and working of Daniel cell. (Oct 08, June 09, June 10)

104. The effective resistances are 10 ohm and 2.4ohm when two resistors are connected in series and in parallel. What are the resistance of individual resistors? (March 07, 10)

105. a) Three resistors are connected is series with 10 V supply as shown in the figure. (June 10)

b) Find the voltage drop across each resistor.

(or)

b) What is the drift velocity of an electron in a copper conductor having area carrying a current of 2 A. Assume that there are 10x10 electrons/m.

106. a) Find the current flowing across three resistors 3 ohm 5 ohm and 2 ohm connected in parallel to a 15 V supply. Also find the effective resistance and total current drawn from the supply. (or) (Oct 10)

b). In a metre bridge, the balancing length for a 10 ohm resistance in left gap is 51.8 cm. Find the unknown resistance and specific resistance of a wire of length 108 cm and radius 0.2 mm
.

106. Applying Wheatstone’s network principle obtain the unknown resistance using metre bridge.

I MID TERM EXPECTED QUESTIONS .LESSONS 1,2,7,& 8 ( 5 MARKS)

2011-08-02T07:31:00.000-07:00

5 MARKS

LESSONS 1 AND 2

80. Write the properties of lines of forces. (Mar 07, Oct 07, Mar 08, 10)

81. Two capacitors of capacitances 0.5 F and 0.75 F are connected in parallel and the combination to a 110 V battery. Calculate the charge from the source and charge on each capacitor. (June 07)

82. Two positive charges of 12 C and 18 C respectively are 10 cm apart. Find the work done in bringing them 4 cm closer, so that they are 6 cm apart. (June 08)

83. Two capacitors of unknown capacitances are connected in series and parallel. If the net capacitances in the two combinations are 6 F and 25 F repectively, find their capacitances. (Oct 08)

84. Define electric potential at a point obtain an expression for electric potential due to a point charge. (March 09)

86. What is electrostatic potential energy of a system of two point charges? (Oct 09)

87. Deduce an expression for the capacitance of a parallel plate capacitor. (June 10)

88. Derive an empression for the torque experienced by an electric dipole when placed in a uniform electric field. (Oct 10)

CURRENT ELECTRICITY

89. Define mobility. Establish a relation between drift velocity and current. (March 06)

90. Obtain the condition for bridge balance in Wheatstones bridge. (Mar 06, June 06, Oct 06, Mar 08, June 09, March 10)

91. State and verify Faraday’s second law of electrolysis. (June 06, March 08)

92. If two or more resistors are connected in parallel, derive an expression for the effective resistance. (Oct 06)

93. How will you compare the e.m.f.s of two cells using a potentiometer? (March 07, Oct; 10)

94. a) In the given network, calculate the effective resistance between points A & B.(March 07)

b) The effective resistances are 10 ohm, 2.4 ohm when they are connected in series and parallel respectively. What are the resistances of individual resistors?

95. Explain the working of a Leclanche cell with a diagram. (June 07)

96. State the explain Kirchhoff’s second law for electrical network. (June 07)

97. Explain the principle of a potentiometer. (Oct 07)

98. Explain the action of lead-acid accumulator. (Oct 07)

99. Explain the determination of the internal resistance of a cell using voltmeter. (June 08, Oct 09)

101. State Faraday’s first law of electrolysis and describe the experimental verification. (June 08, Oct 09)

102. Write any five applications of superconductors. (Oct 08, March 09)

103. Explain the construction and working of Daniel cell. (Oct 08, June 09, June 10)

104. The effective resistances are 10 ohm and 2.4ohm when two resistors are connected in series and in parallel. What are the resistance of individual resistors? (March 07, 10)

105. a) Three resistors are connected is series with 10 V supply as shown in the figure. (June 10)

b) Find the voltage drop across each resistor.

(or)

b) What is the drift velocity of an electron in a copper conductor having area carrying a current of 2 A. Assume that there are 10x10 electrons/m.

b). In a metre bridge, the balancing length for a 10 ohm resistance in left gap is 51.8 cm. Find the unknown resistance and specific resistance of a wire of length 108 cm and radius 0.2 mm.

106. Applying Wheatstone’s network principle obtain the unknown resistance using metre bridge.

I MID TERM EXPECTED QUESTIONS .LESSONS 1,2,7,& 8

2011-08-02T07:27:00.000-07:00

ELECTROSTATICS

1.Define “coulomb” on the basis of coulomb’s law. (Mar.06,oct 10)

2. Why is it safer to be inside a car than standing under a tree during lightning? (Mar 06 June 06 09Mar10)

3. State Gauss’ law in electrostatics.(June 06, Oct 06, Mar09)

4. What is meant by electric polarisation? (or) dielectric polarization. (Oct 06, 09)

5. Define electric potential at a point. (Mar 07, June 09)

6. What is a polar molecule? Give any two examples. (Mar 07)

7. State Coulomb’s law in electrostatics. (June o 07, Mar 10, June 10)

8. What is corona discharge? What are its advantages? (June 07, Oct 08)

9. Write the applications of Capacitor. (Oct 07)

10. What do you mean by “Additive nature of charge”? Give an example. (Oct 07)

11. Three capacitors each of capacitance 9PF are connected in series. What is the total capacitance of the combination, if the combination is connected to 120 V supply? (Mar 08)

12. What is electrostatic shielding ? (Mar 08)

13. Define electric flux. Give its unit (June 08)

14. Explain the working of a microwave oven. (June 08)

15. Calculate the effective capacitance of the combination shown in the figure. (Oct 08)

16. What is an electric dipole? Define electric dipole moment? (Oct 09)

17. What is a capacitor? Define its capacitance?( M ar 09)

18. Mention any three properties of electric lines of force. (June 10)

19. What is non-polar molecule? Give example. (Oct 10)

20. What is an equipotential surface?

21. What is a dielectric and write the effect of dielectric?

CURRENT ELECTRICITY

22. State Ohm’s law. (Mar 06, Oct 07, 09, Mar 10)

23. In the following circuit, calculate the current through the circuit. Mention its direction. (Mar 06)

24. State Faraday’s law ;of electrolysis (Mar 06, June 10, Oct 10)

25. Write any three ;applications of superconductors. (Jkune 06, Oct 06, June 07, Oct 07)

26. A manganin wire of length 2 m has a diameter of 0.4 mm with a resistance of 70 ohm. Find the resistivity of the material. (June 06)

27. State Kircfhhoffs (i) current law and (ii) voltage law. (June 06, March 08)

(or)

State Kirchhoffs second law for electrical network? (March 09)

28. Define mobility of electrons. Write its unit. (Oct 06, Mar 08, 09)

29. Three resistors are connected in series with 10 V supply as shown in the figure. Find the voltage drop across each resistor. (Oct 06, June 10)

30 .State Kirchhoff’s voltage law (Mar 07)

31. Define Drift velocity. (Mar 07, Oct 08, June 09, Oct 09, Mar 10, Oct 10)

32. The resistance of a platinum wire at 0 degree C 4 ohm. What will be the resistance of the wire at 100 degree C if the temperature coefficient of resistance of platinum is 0.0038% C?

33. The resistance of a nichrome wire at 0 degree C is 10 ohm. If its temperature coefficient of resistance is 0.004%C, find its resistance at boiling point of water. Comment on the result.

(June 07, Oct 07, Mar 08, June 09, Oct 10)

34. Define temperatrure coefficient of resistance. (June 08)

35. Distinguish between electric power and electric energy. (June 08, 09)

36. An iron box of 400W power is used daily for 30 minutes. If the cost per unit is 75 paise, find the weekly expense on using the iron box. (June 08)

37 What are the applications of secondary cells? (Oct 08)

38. In the given circuit, what are the total resistance and current supplied by the battery? (Oct 09)

39. Two wires of same material and length have resistances and respectively. Find the ratio of radii of the two wires. (Mar 09)

40. What are the changes observed at transition temperature when the conductor becomes a superconductor? (June 10)

41. Why is copper wire not suitable for a potentiometer

42. Why automobile batteries have low internal resistance.

43. What is electrical Resistivity and conductivity.

44. What are superconductors.

DUAL NATURE OF RADIATION AND MATTER

AND RELATIVBITY

45. What are the limitations of electron microscope? (Mar 06, 09)

46. Write any three uses of photoelectric cells. (June 06, Mar 10, Oct 10)

47. What are intertial and non-inertial frames of reference? (Oct 06, Mar 08)

48. Mention the uses of electron microscope. (Mar 07)

49. What is the de Broglie wavelength of an electron of kinetic energy 120 eV? (June 07, 08)

50. State the postulates of special theory of relativity. (Oct 07, June 09)

51. Calculate the threshold wavelength of certain metal of work function 1.8 e V. (Oct 08)

52. Define stopping potential. (Oct 09)

53. According to classical mechanics, what is the concept of time? (June 10)

54. What is called Frame of reference?

55. What is photoelectric effect?

56. What is Lorentz- Fitzgerald contraction?

57. What are the concepts of time and mass in classical mechanics.

NUCLEAR PHYSICS

58. What is alpha-decay? Give an example. (Mar06)

59. What is pair production and annihilation of matter? (Mar 06, June 06, Mar 07)

60. Write any three properties of neutron. (June 06, Mar 08)

61. Write any three conclusions obtained from Binding energy curve. (Oct 06, Mar 07)

62. Define curie (Oct 06, Mar 08, 10, Oct 10)

63. The half-life of radon is 3.8 days. Calculate its mean life. (Oct 09, June 10)

64. Define roentgen. (June 07, Oct 08)

65. Write a note on Leptons. (June 07)

66. What is the use of a control rod in the reactor? Mention any two control rods. (Oct 07)

67. What are cosmic rays? (June 08, 10)

68. Define critical size and critical mass. (Oct 08)

69. What is meant by breeder reactor? (March 09)

70. Write any three properties of unclear force. (June 08, March 09)

71. How do you classify the neutrons in terms of its kinetic energy? (June 09)

72. What is Binding energy of nucleus? (Oct 09)

73. Tritium has a half-life of 12.5 years. What fraction of the sample will be

left over after 25 years? (March 10)

74. What is mass defect? (Oct 10)

75. What do you mean by artificial radio activity?

76. What are isobars and isotones?

77. Distinguish between natural radioactivity and artificial radioactivity?

How do we know the Age of Things?

2011-07-13T09:19:00.000-07:00

How do we know the Age of Things?

http://youtu.be/w2XBFQKsQEI

G.M.TUBE

2011-07-13T09:16:00.001-07:00

THANKS TO PROVIDERS

G.M.TUBE THANKS TO PROVIDER

2011-07-13T09:12:00.000-07:00

G.M.COUNTER

2011-07-13T09:10:00.001-07:00

SIMPLE G.M.COUNTER

2011-07-13T09:08:00.001-07:00

2011-07-13T09:07:00.001-07:00

BLUE PRINT

2011-07-12T08:31:00.001-07:00

STUDY PLANNER

2011-07-12T08:25:00.001-07:00

STUDY PLANNER

CURRENT ELECTRICITY

2010-11-27T06:38:00.001-08:00

N.SRIRAM.

2. CURRENT ELECTRICITY

1 MARK	3 MARK	5 MARK	10 MARK	TOTAL
1	9	10	--------	20

1.DEFINE "CURRENT ELECTRICITY".

The branch of Physics which deals with the study of motion of

electric charges is called current electricity.

2.DEFINE "EMF" (OR) "ELECTRO MOTIVE FORCE"

The external energy necessary to drive the free

electrons in a definite direction is called electromotive force (emf).

3.DEFINE ELECTRIC CURRENT.WRITE UNIT,EXPRESSION,QTY.

The current is defined as the rate of flow of charges across any

cross sectional area of a conductor. If a net charge q passes through

any cross section of a conductor in time t, then the current I = q / t,

where q is in coulomb and t is in second.

The current I is expressed in ampere.Current is a scalar quantity.

4.DEFINE "DRIFT VELOCITY".WRITE EXPRESSION.

Drift velocity is defined as the velocity with which free electrons

get drifted towards the positive terminal, when an electric field is

applied. vd =aτ

5.DEFINE MOBILITY.
WRITR EXPRESSION.

The mobility is defined as the drift velocity acquired per unit electric field. μ = Vd / E. It takes the unit m²V^–1s^–1.

6.DEFINE "CURRENT DENSITY". WRITE EXPRESSION,UNIT,QTY.

Current density at a point is defined as the quantity of charge

passing per unit time through unit area, taken perpendicular to the

direction of flow of charge at that point.

The current density J for a current I flowing across a conductor

having an area of cross section A is J =(q/t) /A = I/ A

Current density is a vector quantity. It is expressed in A m–2
7.STATE OHM'S LAW.

Ohm's law states that, at a constant temperature, the steady

current flowing through a conductor is directly proportional to the

potential difference between the two ends of the conductor.

(i.e) I α V (or)V = IR .

8. DEFINE RESISTANCE OF A CONDUCTOR.

Resistance of a conductor is defined as the ratio of potential difference across the conductor to the current flowing through it. R =V/I

The unit of resistance is ohm (Ω)

9.DEFINE ELECTRICAL RESISTIVITY.

The electrical resistivity of a material is defined as the resistance offered to current flow by a conductor of unit length having unit area of cross section ρ. =R.A/L.The unit of ρ is ohm−m (Ω m).

10.DEFINE "CONDUCTANCE" AND CONDUCTIVITY".

The reciprocal of resistance is conductance. ρ. = 1/R.

Its unit is mho (Ω–1).

The reciprocal of electrical resistivity, is called electrical

conductivity, σ = 1/ρ. The unit of conductivity is mho m-1 (Ω–1 m–1)

11.DEFINE CONDUCTORS BASED ON RESISTIVITY.

The resistivity of a material is the characteristic of that particular

material. The materials can be broadly classified into conductors and

insulators. The metals and alloys which have low resistivity of the order

of 10⁻⁶ – 10⁻⁸ Ω m are good conductors of electricity. They carry

current without appreciable loss of energy. Example : silver,

aluminium, copper, iron, tungsten, nichrome, manganin, constantan.

12.DEFINE INSULATORS (OR) NON-CONDUCTORS BASED ON RESISTIVITY.

Insulators are substances which have very high resistivity of the order

of 10⁸ – 10¹⁴Ω m. They offer very high resistance to the flow of current

and are termed non−conductors. Example : glass, mica, amber, quartz,

wood, teflon, bakelite.

13.DEFINE SEMICONDUCTORS BASED ON RESISTIVITY.

In between these two classes of materials lie the semiconductors .They are partially conducting. The resistivity of semiconductor is 10⁻² – 10⁴ Ω m. Example : germanium, silicon.

14.What are superconductors,superconductivity?

Ordinary conductors of electricity become better conductors at

lower temperatures. The ability of certain metals, their compounds and

alloys to conduct electricity with zero resistance at very low

temperatures is called superconductivity. The materials which exhibit

this property are called superconductors.

15.Define transition temperature (or) critical temperature.

The temperature at which electrical resistivity of the material suddenly drops to zero and the material changes from normal conductor to a superconductor is called the transition temperature or critical

temperature TC.

16.What are the changes observed at transition temperature?

At the transition temperature the following changes are observed :

(i) The electrical resistivity drops to zero.

(ii) The conductivity becomes infinity

(iii) The magnetic flux lines are excluded from the material.

17.STATE FOUR APPLICATIONS OF SUPERCONDUCTORS

(i) Superconductors form the basis of energy saving power systems, namely the superconducting generators,

(ii) Superconducting magnets have been used to levitate trains above its rails. They can be driven at high speed with minimal expenditure of energy.

(iii) the current in a superconducting wire can flow

without any change in magnitude, it can be used for transmission

lines. (iv) Superconductors can be used as memory or storage

elements in computers.

18.WHAT ARE CARBON RESISTORS ?

Carbon resistor consists of a ceramic core,on which a thin layer of crystalline carbon is deposited. These resistors are cheaper, stable and small in size.

19.WHAT ARE COLOUR CODES IN CARBON RESISTORS?

The resistance of a carbon resistor is indicated by the

colour code drawn on it. Black 0, Brown 1, Red 2,Orange 3,Yellow 4

Green 5, Blue 6,Violet 7,Grey 8,White 9.

20.WHAT IS TOLERANCE?GIVE THE VALUES.

The silver or gold ring at one end corresponds to the tolerance. It is

a tolerable range ( + ) of the resistance. The tolerance of silver,

gold, red and brown rings is 10%, 5%, 2% and 1% respectively. If

there is no coloured ring at this end, the tolerance is 20%.

21.WHAT IS THE EFFECTIVE RESISTANCE OF RESISTORS IN SERIES?

R_S = R₁ + R₂ + R₃

The equivalent resistance of a number of resistors in series

connection is equal to the sum of the resistance of individual resistors.

22.WHAT IS THE EFFECTIVE RESISTANCE OF RESISTORS IN PARALLEL?

When a number of resistors are connected in parallel, the sum of the reciprocal of the resistance of the individual resistors is equal to the reciprocal of the effective resistance of the combination

1/R_P= 1/R₁+1/R₂+1/R₃.

23.DEFINE THE TEMPERATURE DEPENDENCE OF RESISTANCE.

The temperature coefficient of resistance is defined as the ratio of

increase in resistance per degree rise in temperature to its resistance at

0^o C. Its unit is per ^oC. Rt = Ro (1 + αt)

24.DEFINE INTERNAL RESISTANCE OF A CELL

The electric current in an external circuit flows from the positive

terminal to the negative terminal of the cell, through different circuit

elements. In order to maintain continuity, the current has to flow

through the electrolyte of the cell, from its negative terminal to positive

terminal. During this process of flow of current inside the cell, a

resistance is offered to current flow by the electrolyte of the cell. This

is termed as the internal resistance of the cell.

25. STATE KIRCHOFF'S FIRST LAW (CURRENT LAW)

Kirchoff's current law states that the algebraic sum of the currents meeting at any junction in a circuit is zero. The current flowing towards a junction is positive and the current flowing away from the junction

is negative. The sum of the currents entering the junction is equal to the sum of the currents leaving the junction. This law is a consequence of

conservation of charges.

26.STATE KIRCHOFF'S SECOND LAW (VOLTAGE LAW)

Kirchoff's voltage law states that the algebraic sum of the

products of resistance and current in each part of any closed circuit is

equal to the algebraic sum of the emf's in that closed circuit. This law

is a consequence of conservation of energy.

27.DEFINE "ELECTRIC ENERGY" AND "ELECTRIC POWER".

Electric power is defined as the rate of doing electric work.

Power = Work done/ time =VIt/t = VI

Electric power is the product of potential difference and current

strength. Since V = IR, Power = I²R

Electric energy is defined as the capacity to do work. Its unit is

joule. In practice, the electrical energy is measured by watt hour (Wh)

or kilowatt hour (kWh). 1 kWh is known as one unit of electric energy.

1 kWh = 1000 Wh = 1000 × 3600 J = 36 × 10⁵ J

28.WHAT IS WATTMETER?

A wattmeter is an instrument used to measure electrical power

consumed i.e energy absorbed in unit time by a circuit. The wattmeter

consists of a movable coil arranged between a pair of fixed coils in the

form of a solenoid. A pointer is attached to the movable coil. The free

end of the pointer moves over a circular scale. When current flows

through the coils, the deflection of the pointer is directly proportional

to the power.
29.STATE FARADAY'S FIRST LAW OF ELECTROLYSIS

The mass of a substance liberated at an electrode is directly proportional to the charge passing through the electrolyte.

If an electric current I is passed through an electrolyte for a time

t, the amount of charge (q) passed is I t. According to the law, mass of

substance liberated (m) is m α q or m = zIt

where Z is a constant for the substance being liberated called as

electrochemical equivalent. Its unit is kg C–1.

30.DEFINE ELECTROCHEMICAL EQUIVALENT.

The electrochemical equivalent of a substance is defined as the

mass of substance liberated in electrolysis when one coulomb charge

is passed through the electrolyte. m = zIt

where Z is a constant for the substance being liberated called as

electrochemical equivalent. Its unit is kg C–1.

31.STATE STATE FARADAY'S SECOND LAW OF ELECTROLYSIS

The mass of a substance liberated at an electrode

by a given amount of charge is proportional to the *chemical equivalent

of the substance. If E is the chemical equivalent of a substance, from the second law m α E

32.STATE THE APPLICATIONS OF SECONDARY CELLS.

The secondary cells are rechargeable. They have very low internal

resistance. Hence they can deliver a high current if required. They can

be recharged a very large number of times without any deterioration in

properties. These cells are huge in size. They are used in all

automobiles like cars, two wheelers, trucks etc. The state of charging

these cells is, simply monitoring the specific gravity of the electrolyte.

It should lie between 1.28 to 1.12 during charging and discharging

respectively.

FAILURE STUDY PLANNER

2010-11-27T06:09:00.001-08:00

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MARK ALLOTMENT -CUM - BLUE PRINT

LESSON NO	ONE MARK	THREE MARRKS	FIVE MARKS	TEN MARKS	TOTAL
1	4 X 1 = 4	2 X 3 = 6	1 X 5 = 5	1 X 10 = 10	25
2	1 X 1 = 1	3 X 3 = 9	2 X 5 = 10		20
3	2 X 1 =2	1 X 3 = 3	1 X 5 = 5	1 X 10 = 10	20
4	4 X 1 = 4	2 X 3 = 6	1 X 5 = 5	1 X 10 = 10	25
5	4 X 1 = 4	2 X 3 = 6	1 X 5 = 5	1 X 10 = 10	25
6	4 X 1 = 4	2 X 3 = 6	1 X 5 = 5	1 X 10 = 10	25
7	2 X 1 = 2	1 X 3 = 3	2 X 5 = 10		15
8	4 X 1 = 4	2 X 3 = 6	1 X 5 = 5	1 X 10 = 10	25
9	3 X 1 = 3	4 X 3 = 12	1 X 5 = 5	1 X 10 = 10	30
10	2 X 1 = 2	1 X 3 = 3	1 X 5 = 5	1 X 10 = 10	20
NO OF QNS TO BE ANSWERED	30/30	15/20	7/12	4/8	-
PERMITTED TIME (MINUTE)	30	45	45	60	-
STUDY RED MARKED LESSONS	23	51		40	114

MARK ALLOTMENT PHYSICS

2010-11-27T06:08:00.000-08:00

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2010-11-27T05:22:00.000-08:00

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SRIRAM

2010-11-25T08:09:00.001-08:00

		4.Electromagnetic Induction and Alternating Current
	1	Calculate the mutual inductance between two coils when a current of 4A changing to 8A in 0.5 S in one coil. Induces an e.m.f. of 50mV in the other coil.
	2	Mentioned the methods of producing induced e.m.f.
	3	State Faraday's laws of electromagnetic induction.
	4	An aircraft having a wing span of 20.48 m files due north at a speed of 40msֿ1. If the vertical component of earth's magnetic field at the place is 2x10ֿ5T, calculate the e.m.f. induced between the ends of the wings.
	5	Define quality factor.
	6	The wings of an aeroplane are 10 m apart. The Plane is moving horizontally towards the north at a place where the vertical component of earth's magnetic field is 3x10ֿ5 T. Calculate th4e induced e.m.f. set up between the tips of the wings if the velocity of the aeroplane is 720 km/hr.
	7.	State Fleming's right hand rule.
	8	A coil of area of cross-section 0.5m2 with 10 turns is in a plane perpendicular to a uniform magnetic field of 0.2 Wb/m2. Calculate the flux through the coil.
	9	Define r.m.s. value of alternating current.
	10	Why can a.d.c. ammeter not read a.c.?
	11	What is electromagnetic induction?
	12	Give the differences between AF choke and RF choke.
	13	A capacitor of capacitance 2μF is an a.c. circuit to frequency 1000 Hz. If the r.m.s value of the applied e.m.f. is 10V find the effective current flowing in the circuit.
	14	State Lenz's law of electromagnetic induction.
	15	An ideal transformer has transformation ratio9n1: 20 . If the input power and primary voltage are 600 mW and 6V respectively, find the primary and secondary currents.
	16	Define coefficient of self induction.
	17	Calculate the capacitive reactance of a capacitor of capacitance 2μF in an A.C. circuit of frequency 1000Hz. 4.Electromagnetic Induction and Alternating Current

		Part-IV
	1	Explain the principle, construction and theory of a transformer. (diagram not necessary) Define its efficiency. Mention the energy losses.
	2	A source of an alternating e.m.f. is connected to a series combination of a resistor R1, an inductor L and a capacitor C obtain with the help of a voltage phasor diagram and impedance diagram. Expressions for (i) effective voltage(ii) the impedance (iii) phase relationship between the current and voltage.
	3	In an a.c. circuit containing a capacitor the instantaneous e.m.f. is e=E۪ sin ωt. Obtain the expression for instantaneous current. Explain the phase relation between e.m.f. and current by graph..
	4	Describe the principle, construction and working of a single phase a.c. generatior
	5	Discuss with theory the method of inducing e.m.f. in a coil by changing its orientation with respect to the direction of the magnetic field.
	6	Obtain the phase relation between voltage and current in an AC circuit containing a pure inductance. Draw the necessary graph.
	7.	What are eddy currents? Explain their applications. How are they minimized?

2010-11-25T07:59:00.001-08:00

3. Effect of Electric Current

PART I

Mention any two differences between Peltier effect and Joule's heating effect

Define peltier coefficient and write its unit.

Mention the limitations of cyclotron

In a galvanometer, increasing the current sensitivity does not necessarily increase the voltage sensitivity. Explain.

Why is nichrome used as a heating element?

Calculate the resistance of the filaments of a 100W 220V electric bulb.

Define ampere in terms of force between two long parallel current carrying conductors.

Define ampere in terms of force.

What is neutral temperature of a thermocouple?

State Ampere's circuital law.

How is a galvanometer converted into (a) an ammeter. (b) a voltmeter

Part-IV

Apply Biot-Savart law. Obtain an expression for the magnetic induction at a point due to infinitely long straight conductor carrying current.

Derive an expression for the magnetic induction due to an infinitely long straight conductor carrying current. Write the expression for the magnetic induction when the conductor is placed in a medium of permeability μ

Define Ampere's circuital law. Applying it find the magnetic induction due to a long solenoid carrying current.

Explain in detail the principle construction working and limitations of a cyclotron with a diagram.

State Joule's law. . Explain Joule's calorimeter experiment to verify Joule's laws of heating.

Deduce the relation for the magnetic induction at a point along the axis of a circular coil carrying current.

Explain in detail the principle. Construction and theory of a tangent galvanometer

Deduce an expression for the force on a current carrying conductor placed in a magnetic field. Find the magnitude of the force.

SRIRAM

2010-11-25T07:54:00.001-08:00

	2.Current Electricity
1.	State Ohm's law
2	State faraday's laws of electrolysis
3	Write any three applications of superconductors
4	A manganin wire of length 2 m has a diameter of 0.4 mm with a resistance of 70 Ώ Find the resistivity of the material.
5.	State Kirchoff's (i) current law and (ii)voltage law
6	State kirchoff's voltage law.
7	Define mobility of electrons . Give its unit
8	Define drift velocity.
9	The resistance of a platinum wire at 0c is 4Ω what will be the resistance of the wire at 100c if the temperature coefficient of resistance of platinum is 0.0038/c?
	Distinguish between electromotive force and potential difference
11	The resistance of a nichrome wire at 0c is 10Ω it is temperature coefficient of resistance is 0.004/c. find its resistance at boiling point of water. Comment on the result.
.12	Define temperature coefficient of resistance.
13	Distinguish between electric power and electric energy
14	An iron box of 400 w power is used daily for 30 minutes. If the cost per unit is 75 paise . find the weekly expense on using the iron box.
15	What are the applications of secondary cells
16	Two wires of same material and length have resistance 5Ω and 10Ω respectively. Find the ratio of radii of the two wires.
17	State Kirchhoff's second law for electrical network.

1. Electrostatics PART I

2010-11-25T07:38:00.001-08:00

1	Define Coulomb on the basis of Coulomb' s law
2	Why is it safer to be inside a car than standing under a tree during lightning?
3	State Gauss law in electrostatics?
4	What is meant by electric polarisation?
5	Define electric potential at a point
6	What is a polar molecule? Given any two examples
7	State Coulomb' s law in electrostatics
8	What is Corona discharge? What are its advantages?
9	Writer the application of capacitor
10	What do you mean by 'Additive nature of charge'? Given an example
11	Three capacitors each of capacitance 9 Pf are connected in series. What is the total capacitance of the combination ?
12	What is electrostaic shielding?
13	Define electric flux. Give its unit
14	Explain the working of a microwave oven
15	What is capacitor? Define its capacitance.

DISCHARGE TUBE

2009-10-29T06:41:00.002-07:00

ATOMIC PHYSICS

2009-10-29T06:33:00.000-07:00

2009-10-03T07:05:00.000-07:00

slide show sriram

10. Communication Systems

2009-06-27T05:22:00.001-07:00

10. Communication Systems
1.What are the different ways of propagation of radio waves?
Radio wave is propagated from the transmitting to the receiving
antenna mainly in three different ways depending on the frequency of
the wave. They are :
(i) Ground (surface) wave propagation
(ii) Space wave propagation
(iii) Sky wave (or) ionospheric propagation
2.Define: Ground or surface wave propagation
Ground or surface waves are the radio waves which travel along the surface of the earth. Ground wave propagation takes place when the transmitting and receiving antennas are close to the ground. Ground wave propagation is of prime importance only for medium and long wave signals. All medium wave signals received during the daytime use surface wave propagation.
3.Define Space wave propagation
Radio waves propagated through the troposphere of the Earth are
known as space waves. Troposphere is the portion of the Earth’s
atmosphere which extends upto 15 km from the surface of the Earth.
Space wave usually consists of two components :(i) A component which travels straight from the transmitter to the receiver.
(ii) A component which reaches the receiver after reflection from
the surface of the Earth. Space wave propagation is particularly suitable for the waves having frequency above 30 MHz.
4.How ionospheric layer formed.
The ionosphere is the upper portion of the atmosphere, which absorbs large quantities of radiant energy like ultra violet rays, cosmic rays etc., from the sun, becoming heated and ionised. This ionized region contains free electrons, positive and negative ions. The ionosphere is the upper portion of the atmosphere, which absorbs large quantities of radiant energy like ultra violet rays, cosmic rays etc., from the sun, becoming heated and ionised. This ionized region contains free electrons, positive and negative ions.
5.Define Sky wave (or) ionospheric propagation
Radio waves in the short wave band, radiated from an antenna at large angles with ground, travel through the atmosphere and encounters the ionised region in the upper atmosphere. Under favourable circumstances, the radiowaves get bent downwards due to refraction from the different parts of the ionised region and again reach the earth at a far distant point. Such a radio wave is called the sky wave and such a propagation of radio wave is known as sky wave propagation or ionospheric propagation. Long distance radio communication is thus possible through the sky wave propagation.
6.Define :Skip distance and skip zone
In the skywave propagation, for a fixed frequency, the shortest
distance between the point of transmission and the point of reception
along the surface is known as the skip distance.The minimum distance between the transmitter and the ray which strikes the ground (ie)Earth is called as the skip distance.
The region between the point where there is no reception of
ground waves and the point where the sky wave is received first is
known as skip zone. In the skip zone, there is no reception at all.
7.What is Modulation and Demodulation?
This process of changing of amplitude or frequency or phase of the carrier wave in accordance with the intensity of the signal is known as modulation.. Some of the modulation process namely,(i) amplitude modulation, (ii) frequency modulation and (iii) phase modulation are discussed.
At the receiver end, the audio signal is extracted from the modulated wave by the process called demodulation.
8.Define Amplitude modulation (AM)
When the amplitude of high frequency carrier wave is changed in
accordance with the intensity of the signal, the process is called
amplitude modulation.
9.Define Modulation factor
Modulation factor is defined as the ratio of the change
of amplitude in carrier wave after modulation to the amplitude of the
unmodulated carrier wave.
i.e. modulation factor, m = Amplitude change of carrierwave after modulation/Amplitude of carrier wave before modulation
m =Signal amplitude/Carrier amplitude
10.Define channel width.
The channel width is given by the difference between extreme
frequencies i.e. between maximum frequency of USB and minimum
frequency of LSB.
Channel width = 2 × maximum frequency of the modulating signal;
= 2 × (fs)max
11.State the Advantages and limitations of amplitude modulation.
(i) Easy transmission and reception
(ii) Lesser bandwidth requirements
(iii) Low cost
Limitations
Noisy reception .Low efficiency . Small operating range

12.Explain limitation or demerits in A.M.wave.
In an AM wave, the signal appears in the
amplitude variations of the carrier. Practically, all the natural and man
made noises consists of electrical amplitude disturbances. As a radio
receiver cannot distinguish between amplitude variation that represent
noise and those that contain the desired signal, the reception is
generally noisy.
(ii) Low efficiency : In AM, useful power is available in the side
bands, since they contain signals. The sideband power for an AM wave
is low. Hence the efficiency of AM is low.
(iii) Small operating range : Due to low efficiency of amplitude
modulation, transmitters employing this method have a small operating
range i.e. the messages cannot be transmitted over long distances.
13.Define Frequency modulation (FM)
When the frequency of carrier wave is changed in accordance with
the intensity of the signal, the process is called frequency modulation.
In frequency modula-tion, the amplitude and phase of the carrier
wave remains constant. Only, the frequency of the carrier wave is
changed in accordance with the signal.
14.Define resting frequency and carrier swing.
The frequency of an FM transmitter without signal input is called the resting
frequency or centre frequency (fo ) and this is the allotted frequency of the transmitter. When the signal is applied, the carrier frequency deviates up and down from its resting value fo.
The change or shift either above or below the resting frequency is
called frequency deviation (Δf). The total variation in frequency from the
lowest to the highest is called carrier swing (CS). Hence,
Carrier swing = 2 × frequency deviation = 2 × Δf
15.What are the advantages of F.M.waves?
(i) It gives noiseless reception. Noise is a form of amplitude
variation and a FM receiver will reject such noise signals.
(ii) The operating range is quite large.
(iii) The efficiency of transmission is very high.
Disadvantages
(i) A much wider channel is required by FM.
(ii) FM transmitting and receiving equipments tends to be more complex.
16.Define : Phase modulation (PM)
In phase modulation, the phase of the carrier wave is varied in
accordance with the amplitude of the modulating signal and the rate of
variation is proportional to the signal frequency. The waveform of the
phase modulated wave is similar to that of FM wave. The phase
modulation, generally uses a smaller bandwidth than FM.
17.What is an antenna?
An antenna is a long conductor (wire and rod) that acts as a conversion device. It converts an electrical signal into electromagnetic energy when used as a transmitting antenna. In receiving antenna, the electromagnetic energy is converted into an electrical signal. An antenna is characterised by an important parameter,directivity.
18.Define directivity of an antenna.
Directivity is the ability of the antenna to concentrate the
electromagnetic waves in the most desired directions (during
transmission) or to have maximum reception from most preferred
directions (during reception).
19.Define Scanning .
Scanning is the process by which an electron beam spot is made to
move across a rectangular area, so as to cover it completely. This
rectangular area may be the target surface in a television camera or the
screen of a picture tube in a television receiver.
For scanning the picture elements, saw tooth potentials can be
used. Saw tooth potentials are produced by using a unijunction
transistor and a R-C network. Saw tooth potentials are applied to
horizontal and vertical deflector plates in a TV camera.
20.Define Interlaced scanning
In this scanning, the total number lines are divided into two groups called fields. During the presentation of the first field, only the odd numbered lines are scanned, while during the second field all the even numbered lines are scanned. Half way along the bottom of the first field, the vertical retrace returns the scanning beam to the top of the image and completes the unfinished lines. (i.e) The remaining even numbered lines are then scanned during second field. This method of scanning is known as interlaced scanning.
21.What is RADAR?State the principle.
The term RADAR is an acronym for RAdio Detection And
Ranging. It is a system which uses radio waves to detect and to fix the
position of targets at a distance
Principle of radar
Radar works on the principle of ‘radio echoes’. The transmitter in a radar, radiates the high power electrical pulses into space. When these pulses are incident on any distant target such as a mountain, ship or aircraft, they get scattered in all directions. The transmitter antenna receives a part of the scattered energy. This transmitter antenna also acts as receiving antenna for the receiving pulse.
22.State the applications of radar.
(i) Air and sea navigation is made entirely safe, with radar installations. High flying planes and ship at sea, can get detailed reports of mountains, ice bergs, rivers, lakes, shore lines etc., which they can avoid.
(ii) Radar systems are used for the safe landing of air crafts. On approaching the air field, the pilot is guided by signals from a radar set,
so that it flies along the line of the runway and lands safely, whatever
be the visibility.
(iii) Rain drops may reflect suitable radar signals and thus enable
meteorologists to measure the distance of the clouds, with great
accuracy for forecasting.
(iv) The pulses can be used for discovering the position of buried
metals, oils and ores.
23.Define : Analog communication
In analog communication, analog signals are used. An analog signal is a continuously varying voltage or current. Traditionally, in telephone and radio systems, the messages consisted of information conveyed by voice. The voice signal is an analog signal and so could take on any value within the overall range allowed. For example, if the telephone system were set up to handle voice signals, which ranged from 0 to 1 volt, the values transmitted at any instant could be 0.345 V, 0.179 V, and so on. This is called analog signal
communication, because the signal can be any value within the range.
24.Define : Digital Communication
A digital communication system offers many advantages to the
user, that cannot be achieved with an analog system. Digital
communications system may make use of analog links and concepts.
A digital system is a more general case of a binary system. In
binary system, only two signal values can exist. They are often called
0 and 1, but these names represent specific voltages.
25.List the advantages & disadvantages of digital communication.
(i) The transmission quality is high and almost independent of
the distance between the terminals.
(ii) The capacity of the transmission system can be increased.
(iii) The newer types of transmission media such as light beams
in optical fibers and wave guides operating in the microwave frequency
extensively use digital communication.
Disadvantages
(i) A digital system requires larger bandwidth.
(ii) It is very difficult to gradually change over from analog to
digital transmission.
26.What is Modem?
The name modem is the abbreviation of the term Modulator and
Demodulator. As the name implies, both functions are included in a
modem. A modem is used to convert digital signals into analog signals
capable of being transmitted over telephone lines. At the receiving end
of the system, modem is used to demodulate the analog signals and
reconstruct the equivalent digital output. Modems are placed at both
ends of the communication circuit
27. Fiber optical communication
Coherent light can be generated with laser or light emitting diodes and may be detected by photo-diodes. Optical fibers are used for transmission of light. An optical fiber is a thin transparent rod, usually made of glass or plastic, through which light can propagate. The light signals travel through the rod from the transmitter to the receiver and can be easily detected at the receiving end of the optical fiber. The principle of total internal reflection is used for the transmission of light signals through the optical fiber.
28.State the advantages& applications of fibre optical communication.
(i) Transmission loss is low. (ii) Fiber is lighter and less bulky than equivalent copper cable. (iii) More information can be carried by each fiber than by
equivalent copper cables.(iv) There is no interference in the transmission of light from electrical disturbances or electrical noise.
Applications
The various applications of fiber in communication area are,
voice telephones, video phones, message services, data network etc.
29.State the merits of satellite communication.
(i) Mobile communication can be easily established by satellite
communication.
(ii) Satellite communication is economical compared with
terrestrial communication particularly where long distances are
involved.
(iii) Compared to the optical fiber communication, satellite
communication has the advantages that, quality of transmitted signal
and location of sending and receiving stations are independent of
distance.
(iv) For thin traffic remote areas like north east regions in India,
Ladakh etc., satellite communication is most economical.
(v) For search, rescue and navigation, satellite communication is
far superior and economical compared to other systems.
30.State the demerits of satellite communication.
(i) Between talks there is a time gap which becomes quite
annoying. This time delay also reduces the efficiency of satellite in data
transmission.
(ii) An imperfect impedance match may cause echo, received
back after a delay. Echo suppressor has to be used.
(iii) Repair of satellite is almost impossible, once it has been
launched.

9. Semiconductor Devices and their Applications

2009-06-27T05:19:00.000-07:00

9. Semiconductor Devices and their Applications
1.Define semiconductors.
A material which has resistivity between conductors and insulators is
known as semiconductor. The resistivity of a semiconductor lie
approximately between 10-2 and 104 Ω m at room temperature.
Germanium and silicon are most widely used as semiconductors.
2.Define Valance band.
A band which is occupied by the valence electrons or a band having highest
energy is defined as valence band .
3.Define: Forbidden energy gap.
The separation between valence band and conduction band is
known as forbidden energy gap. The forbidden gap energy is of the order of 0.7eV for Ge and 1.1eV for Si.
4.Define intrinsic and extrinsic semiconductors.
A semiconductor which is pure and contains no impurity is
known as an intrinsic semiconductor. In an intrinsic semiconductor,
the number of free electrons and holes are equal. Common examples
of intrinsic semiconductors are pure germanium and silicon.
The process of addition of a very small amount of impurity into an intrinsic semiconductor is called doping. The impurity atoms are called dopants. The semiconductor containing impurity atoms is known as impure or doped or extrinsic semiconductor.
5.State the methods of doping a semiconductors.
There are three different methods of doping a semiconductor.
(i) The impurity atoms are added to the semiconductor in its
molten state.
(ii) The pure semiconductor is bombarded by ions of impurity
atoms.
(iii) When the semiconductor crystal containing the impurity
atoms is heated, the impurity atoms diffuse into the hot crystal.
6.How N-type semiconductor formed?
When a small amount of pentavalent impurity such as arsenic is
added to a pure germanium semiconductor crystal, the resulting crystal
is called N-type semiconductor.
7.How P-type semiconductor formed?
When a small amount of trivalent impurity (such as indium,
boron or gallium) is added to a pure semiconductor crystal, the
resulting semiconductor crystal is called P-type semiconductor.
8.What is forward bias condition?
When the positive terminal of the battery is connected to P-side and negative terminal to the N-side, so that the potential difference acts in opposite direction to the barrier potential, then the PN junction diode is
said to be forward biased.
9.What is reverse bias condition?
When the positive terminal of the battery is connected to the N-side and negative terminal to the P-side, so that the applied potential difference is in the same direction as that of barrier potential, the junction is said to be reverse biased.
10.What is rectifier & rectification?
The process in which alternating voltage or alternating current is
converted into direct voltage or direct current is known as rectification.
The device used for this process is called as rectifier. The junction diode
has the property of offering low resistance and allowing current to flow
through it, in the forward biased condition. This property is used in the
process of rectification.
11.Define Avalanche breakdown
When both sides of the PN junction are lightly doped and the depletion layer becomes large, avalanche breakdown takes place. In this case, the electric field across the depletion layer is not so strong. The minority carriers accelerated by the field, collide with the semiconductor atoms in the crystal. Because of this collision with valence electrons, covalent bonds are
broken and electron hole pairs are generated. These charge carriers, so
produced acquire energy from the applied potential and in turn produce
more and more carriers. This cumulative process is called avalanche
multiplication and the breakdown is called avalanche breakdown.
12.Define: Zener breakdown : When both sides of the PN junction are
heavily doped, consequently the depletion layer is narrow. Zener
breakdown takes place in such a thin narrow junction. When a small
reverse bias is applied, a very strong electric field is produced across
the thin depletion layer. This field breaks the covalent bonds,
extremely large number of electrons and holes are produced, which
give rise to the reverse saturation current (Zener current). Zener
current is independent of applied voltage.
13.What are the different layers of transistors?
Base (B) layer : It is a very thin layer, the thickness is about
25 microns. It is the central region of the transistor.
(ii) Emitter (E) and Collector (C) layers : The two layers on the
opposite sides of B layer are emitter and collector layers.
14.What are the bias condition for a transistor to work?
For a transistor to work, the biasing to be given are as follows :
(i) The emitter-base junction is forward biased, so that majority
charge carriers are repelled from the emitter and the junction offers
very low resistance to the current.
(ii) The collector-base junction is reverse biased, so that it
attracts majority charge carriers and this junction offers a high
resistance to the current.

15.What are Transistor circuit configurations?
There are three types of circuit connections (called configurations or modes) for operating a transistor. They are (i) common base (CB) mode
(ii) common emitter (CE) mode and (iii)common collector (CC) mode.
16.Write note on:Transistor amplifier
The important function of a transistor is the amplification. An
amplifier is a circuit capable of magnifying the amplitude of weak
signals. The important parameters of an amplifier are input
impedance, output impedance, current gain and voltage gain. A good
design of an amplifier circuit must possess high input impedance, low
output impedance and high current gain.
17.What is Multistage amplifiers?
The amplification of a signal by a single amplifier may not be enough in most of the practical cases. Hence in these cases, two or more amplifiers are used in series to get sufficient amplified signal. The amplifiers are coupled in such a manner that the output of the first stage becomes the input for the next stage. Connecting the amplifiers in this manner is known as cascading the stages. When a number of amplifiers are connected in cascade, the overall voltage gain is equal to the product of voltage gain of individual stages. This is known as multistage amplifiers.
18.What is Feedback in amplifiers?State its types.
Feedback is said to exist in an amplifier circuit, when a fraction of the
output signal is returned or fed back to the input and combined with
the input signal. If the magnitude of the input signal is reduced by the
feed back, the feed back is called negative or degenerative. If the
magnitude of the input signal is increased by the feed back, such feed
back is called positive or regenerative.
19.What are the advantages of negative feedback?
The advantages of negative feedback are,
(i) Highly stabilised gain. (ii) Reduction in the noise level.
(iii) Increased bandwidth (iv) Increased input impedance and decreased output impedance. (v) Less distortion.
20.State “ Barkhausen condition” for oscillation
The gain of the amplifier with positive feedback is given by
Af =A/( 1 − A β), where A is the voltage gain without feedback, β isthe feedback ratio and Aβ is the loop gain. When Aβ = 1, thenAf= ∞. This means that output voltage is obtained, even if input voltage is zero, (i.e) it becomes an oscillator. The essential condition for the maintenance of oscillation is
Aβ = 1. This condition means that (i) the loop gain Aβ = 1 and (ii) the net phase shift round the loop is 0o or integral multiples of 2π.
These are called the Barkhausen conditions for oscillations.
21.What is Integrated circuit (IC)?
An integrated circuit (IC) consists of a single – crystal chip of
silicon, containing both active (diodes and transistors) and passive
(resistors, capacitors) elements and their interconnections.
22.What are the advantages of ICs?
(i) Extremely small in size (ii) Low power consumption
(iii) Reliability (iv) Reduced cost
(v) Very small weight (vi) Easy replacement
23.What are the types of ICs?
Digital ICs : The integrated circuits which process
the digital signals are called digital ICs.
Linear ICs : The integrated circuits which process
the analog signals are called linear ICs.
24.What are Analog signals?
The signal current or voltage is in the form of continuous, time varying voltage or current (sinusoidal). Such signals are called
continuous or analog signals.
25.What are Logic gates?
Circuits which are used to process digital signals are called logic gates. They are binary in nature. Gate is a digital circuit with one or more inputs but with only one output. The output appears only for certain combination of input logic levels. Logic gates are the basic building blocks from which most of the digital systems are built up. The numbers 0 and 1 represent the two possible states of a logic circuit. The two states can also be referred to as ‘ON and OFF’ or ‘HIGH and LOW’ or ‘TRUE and FALSE’.
26.Explain :OR gate
An OR gate has two or more inputs but only one output. It is
known as OR gate, because the output is high if any one or all of the
inputs are high. The logic symbol of a two input OR gate is shown in
Fig .The Boolean expression to represent OR gate is given by Y= A+B
27.Explain AND gate
An AND gate has two or more inputs but only one output. It is
known as AND gate because the output is high only when all the
inputs are high. The logic symbol of a two input AND gate is shown
in Fig.
The Boolean expression to represent AND gate is given by
Y = A . B ( . should be read as AND)
28.Explain NOT gate (Inverter)
The NOT gate is a gate with only one input and one output. It is
so called, because its output is complement to the input. It is also
known as inverter. Fig shows the logic symbol for NOT gate.
The Boolean expression to represent NOT operation is Y = A .
29.Explain NAND gate
This is a NOT–AND gate. It can be obtained by connecting a NOT
gate at the output of an AND gate.
The logic symbol for NAND gate is shown in Fig .
The Boolean expression to represent NAND Operation is Y = AB
30.Explain NOR gate
This is a NOT–OR gate. It can be made out of an OR gate by
connecting an inverter at its output .
The logic symbol for NOR gate
The Boolean expression to represent NOR Operation is Y = A + B
31.Write De-Morgan’s theorems
The two De Morgan’s theorems are,
First theorem
“The complement of a sum is equal to the product of the
complements.” If A and B are the inputs, then A+B=A . B
Second theorem
“The complement of a product is equal to the sum of the
complements.” If A and B are the inputs, then A . B=A+B.
32.Why NAND and NOR gates are known as Universal gates?
NAND and NOR gates are called Universal gates because they can
perform all the three basic logic functions. The construction of basic logic gates NOT, OR and AND using NAND and NOR gates is also easy.
33.State the basic Laws and theorems of Boolean algebra.
Basic laws :Commutative laws:
A + B = B + A; and AB = BA
Associative Laws
A + (B + C) = (A + B) + C and A (BC) = (AB) C
Distributive law
A (B+C) = AB + AC
New operations :
A + 0 = A; A + 1 = 1; A.0 = 0; A.1 = A
A + A = A;A + A = 1;A.A = A
A . A = 0; A = A.
34.What are Operational amplifiers (OP – AMP)?
OP-AMP is a solid state device capable of sensing and amplifying
dc and ac input signals. OP-AMP is an amplifier with two inputs
(differential inputs) and a single output. OP-AMP consists of 20
transistors, 11 resistors and one capacitor.
35.What are the characteristics of OP – AMP?
The most important characteristics of OP-AMP are : (i) very high
input impedance or even infinity which produces negligible current at
the inputs, (ii) very high gain, (iii) very low output impedance or even
zero, so as not to affect the output of the amplifier by loading.
36.State the uses of Cathode ray oscilloscope (CRO)?
(i) It is used to measure a.c and d.c voltage.
(ii) It is used to study the waveforms of a.c voltages.
(iii) It is used to find the frequency of a.c voltage.
(iv) It is used to study the beating of heart in cardiology.
37.What is a Multimeter?
Multimeter is an electronic instrument, which is used to
measure voltage, current and resistance. This is called as AVO meter
(ampere, voltage, ohm)(i)as a voltmeter
The moving coil galvanometer is converted into a voltmeter by
connecting in series a high resistance of suitable value
(ii) as an ammeter
The galvanometer is converted into an ammeter by shunting it
with suitable low resistances, one for each range
(iii)as an ohm-meter
The galvanometer is converted into an ohm-meter by connecting
a battery and a suitable resistance in series

8. Nuclear Physics

2009-06-27T05:03:00.000-07:00

8. Nuclear Physics

1.What are Isotopes?Give examples.
Isotopes are atoms of the same element having the same atomic
number Z but different mass number A. The nuclei 1H1, 1H2 and 1H3
are the isotopes of hydrogen. In other words isotopes of an element
contain the same number of protons but different number of neutrons.
2.What are Isobars?Give examples.
Isobars are atoms of different elements having the same mass
number A, but different atomic number Z. The nuclei 8O16 and 7N16
represent two isobars.
3.What are Isotones?Give examples.
Isotones are atoms of different elements having the same number
of neutrons. 6C14 and 8O16 are some examples of isotones.
4.Define : “One atomic mass unit”
One atomic mass unit is considered as one twelfth of the mass of carbon atom 6C12. Carbon of atomic number 6 and mass number 12 has mass equal to 12 amu. 1 amu = 1.66 × 10−27 kg.
5.Calculate energy equivalence of one amu in electron-volt.
Einstein’s mass energy relation is, E = mc2
Here, m = 1 amu = 1.66 × 10−27 kg,c = 3 × 108 ms−1
E = 1.66 × 10−27 × (3 × 108)2 J
One electron-volt (eV) is defined as the energy of an electron when
it is accelerated through a potential difference of 1 volt.
1 eV = 1.6 × 10−19 coulomb × 1 volt 1 eV = 1.6 × 10−19 joule
eV = 931 × 106 eV = 931 million electronvolt = 931 MeV
Thus, energy equivalent of 1 amu = 931 MeV.
6.Define mass defect.
The difference in the total mass of the nucleons and the
actual mass of the nucleus is known as the mass defect.
mass of a nucleus, m < (Zmp + Nmn) Zmp + NmN – m = Δm, where Δm is the mass defect
7. Define : Binding Energy
When the protons and neutrons combine to form a nucleus, the mass that disappears (mass defect, Δm) is converted into an equivalent amount of energy (Δmc2). This energy is called the binding energy of the nucleus. Binding energy = [ZmP + Nmn – m] c2 = Δm c2 The binding energy of a nucleus determines its stability against disintegration.
8.Define Nuclear force
There is some force in the nucleus which overcomes the electrostatic repulsion between positively charged protons and binds the protons and neutrons inside the nucleus. This force is called nuclear force.
9.Define :Radioactivity (or) natural radioactivity.
The phenomenon of spontaneous emission of highly penetrating radiations such as α, β and γ rays by heavy elements having atomic number greater than 82 is called radioactivity and the substances which emit these radiations are called radioactive elements.
10.State four properties of α–rays
(i) An α - particle is a helium nucleus consisting of two protons and two neutrons. It carries two units of positive charge. (ii) They move along straight lines with high velocities. (iii) They are deflected by electric and magnetic fields. (v) They affect photographic plates. (vi) They are scattered by heavy elements like gold. (vii) They produce fluorescence when they fall on substances like zinc sulphide or barium platinocyanide.
11.State four Properties of β – rays
(i) β–particles carry one unit of negative charge and mass equal to that of electron.Therefore, they are nothing but electrons. (ii) The β–particles emitted from a source have velocities over the range of 0.3 c to 0.99 c, where c is the velocity of light. (iii) They are deflected by electric and magnetic fields. (iv) The ionisation power is comparatively low (v) They affect photographic plates. (vi) They penetrate through thin metal foils and their penetrating power is greater than that of α−rays (vii) They produce fluorescence when they fall on substances like barium platinocyanide.
12.State four Properties of γ – rays.
(i) They are electromagnetic waves of very short wavelength. (ii) They are not deflected by electric and magnetic fields. (iii) They travel with the velocity of light. (iv) They produce very less ionisation. (v) They affect photographic plates. (vi) They have a very high penetrating power, greater than that of β-rays.(vii) They produce fluorescence. (viii) They are diffracted by crystals in the same way like X−rays are diffracted.
13.State Radioactive displacement law for α-decay.
When a radioactive nucleus disintegrates by emitting an α-particle, the atomic number decreases by two and mass number decreases by four. The α-decay can be expressed as zXA à z−2YA−4 + 2He4 93 Example : Radium (88Ra226) is converted to radon (86Rn222) due to α−decay 88Ra226 à 86Rn222 + 2He4
14.State Radioactive displacement law for β−decay
When a radioactive nucleus disintegrates by emitting a β− particle, the atomic number increases by one and the mass number remains the same. β−decay can be expressed as zXA à Z+1YA + −1e0 Example : Thorium (90Th234) is converted to protoactinium (91Pa234) due to β−decay => 90Th234 à 91Pa234 + −1e0
15.State Radioactive displacement law for γ−decay
When a radioactive nucleus emits γ−rays, only the energy level
of the nucleus changes and the atomic number and mass number
remain the same. During α or β− decay, the daughter nucleus is mostly in
the excited state. It comes to ground state with the emission of γ−rays.
Example : During the radioactive disintegration of radium (88Ra226)
into radon (86Rn222), gamma ray of energy 0.187 MeV is emitted, when
radon returns from the excited state to the ground state .
16.State Radioactive law of disintegration (or) Rutherford and Soddy law
Rutherford and Soddy found that the rate of disintegration is
independent of physical and chemical conditions. The rate of
disintegration at any instant is directly proportional to the number of
atoms of the element present at that instant. This is known as
radioactive law of disintegration.
N = N0 e−λt
17.Define “half life period” of a radioactive element.
The half life period of a radioactive element is defined as the time
taken for one half of the radioactive element to undergo disintegration.
T½= 0.6931/λ
18.Define “mean life period” of a radioactive element.
The mean life of a radioactive substance is defined as the ratio
of total life time of all the radioactive atoms to the total number of
atoms in it.
Mean life =Sum of life time of all the atoms/Total number of atoms
τ =1/λ λ = 0.6931 τ

19.Define “curie”
The activity of a radioactive substance is generally expressed in
curie. Curie is defined as the quantity of a radioactive substance which
gives 3.7 × 1010 disintegrations per second or 3.7 × 1010 becquerel. This
is equal to the activity of one gram of radium.
20.Classify neutrons based on kinetic energes.
Neutrons are classified according to their kinetic energy as
(a) slow neutrons and (b) fast neutrons. Both are capable of penetrating
a nucleus causing artificial transmutation of the nucleus.
Neutrons with energies from 0 to 1000 eV are called slow neutrons. The neutrons with an average energy of about 0.025 eV in thermal equilibrium are called thermal neutrons. Neutrons with energies in the range between 0.5 MeV and 10 MeV are called fast neutrons.
21.Define : Artificial radioactivity
The phenomenon by which even light elements are made
radioactive by artificial or induced methods is called artificial
radioactivity.
5B10 + 2He4 à 7N13* + 0n1
7N13* à 6C13 + 1e0
13Al27 + 2He4 à 15P30* + 0n1

22.State the methods of production of artificial radio-isotopes
(i) Artificial radio-isotopes are produced by placing the target
element in the nuclear reactor, where plenty of neutrons are available.
(1) 15P31 + 0n1 à 15P32* + γ, and (2) 11Na23 + 0n1 à 11Na24* + γ
(ii) Another method of production of artificial radio-isotope is to
bombard the target element with particles from particle accelerators
like cyclotron.
11Na23 + 1H2 à 11Na24* + 1H1

23.State the applications of radio-isotopes in medical field.
Radio cobalt (Co60) --treatment ofcancer. Radio-sodium (Na24)-- detect the presence of blocks in blood vessels, to check the effective functioning of heart in pumping blood and maintaining circulation.
Radio-iodine (I131) ---detection of thyroid gland and also for treatment
& also used to locate brain tumours. Radio-iron (Fe59) --- diagnose anaemia.. Radio-phosphorous (P32) ---treatment of skin diseases.
24.State the applications of radio-isotopes in Agriculture field.
In agriculture, radio-isotopes help to increase the crop yields.
Radio-phosphorous (P32) incorporated with phosphate fertilizer is added
to the soil. The plant and soil are tested from time to time. Phosphorous is taken by the plant for its growth and radio-phosphorousis found to increase the yield.
Sprouting and spoilage of onions, potatoes, grams etc. are
prevented by exposure to a very small amount of radiation. Certain
perishable cereals remain fresh beyond their normal life span when
exposed to radiation.
25.State the applications of radio-isotopes in Industrial field and Molecular biology
In Industry, the lubricating oil containing radio-isotopes is used
to study the wear and tear of the machinery.
In molecular biology radio-isotopes are used in sterilising
pharmaceutical and surgical instruments.
26.What is Radio-carbon dating ?
Living things take C14 which is radioactive, from food and air. However with death,the intake of C14 stops, and begins to decay. Hence the amount of C14 in the sample will enable the calculation of time of death i.e, the age of the specimen could be estimated. This is called
radio-carbon dating, employed in the dating of wooden implements, leather clothes, charcoal used in oil paintings, mummies and so on.

27.What are the biological effects of nuclear radition?
The biological effects of nuclear radiation can be divided into three
Groups (i) Short term recoverable effects (ii) long term irrecoverable effects and (iii) genetic effect
28.What are the factors that a human organism affected by radiation depends?
The extent to which the human organism is damaged depends
upon (i) the dose and the rate at which the radiation is given and
(ii) the part of the body exposed to it.
29.What are the precautions to be taken while working radiation labs?
The following precautions are to be taken for those, who are
working in radiation laboratories.
(1) Radioactive materials are kept in thick−walled lead
container. (2) Lead aprons and lead gloves are used while working in
hazardous area. (3) All radioactive samples are handled by a remote control process. (4) A small micro−film badge is always worn by the person and it is checked periodically for the safety limit of radiation.
30.Define: “Roentgen”:
The radiation exposure is measured by the unit called roentgen (R). One
roentgen is defined as the quantity of radiation which produces 1.6 × 1012 pairs of ions in 1 gram of air.
31.What is meant by artificial transmutation?
Artificial transmutation is the conversion of one element into
another by artificial methods.
When nitrogen was bombarded with α-particles of sufficient energy, a rare isotope of oxygen (8O17) and a proton were formed.
7N14 + 2He4 à 8O17 + 1H1
32.What are Particle accelerators?
A particle accelerator is a device used to accelerate the charged
particles, which are required in the study of artificial transmutation of
elements.
(i) The first type belongs to electrostatic accelerators :The Cockcroft – Walton and Van de Graaff generators
(ii) The second type is the cyclic or synchronous accelerator: Linear accelerator, cyclotron, betatron,synchrocyclotron and synchrotron.
33.Define :Nuclear fission
The process of breaking up of the nucleus of a heavier atom into
two fragments with the release of large amount of energy is called
nuclear fission.
92U235 + 0n1 à 56Ba141 + 36Kr92 + 3 0n1 + Q
34.Define: Chain reaction
A chain reaction is a self propagating process in which the number of neutrons goes on multiplying rapidly almost in a geometrical progression.
35..Define: Critical size
Critical size of a system containing a fissile material is defined as the minimum size in which atleast one neutron is available for further fission reaction. The mass of the fissile material at the critical size is called critical mass. The chain reaction is not possible if the size is less than the critical size.
36.What is nuclear reactor?
A nuclear reactor is a device in which the nuclear fission
reaction takes place in a self sustained and controlled manner. The
first nuclear reactor was built in 1942 at Chicago USA.
· Research reactors -supply neutrons for research purpose and for production of radio-isotopes.
· Production reactors - convert fertile (non-fissile but abundant)
material into fissile material.
· The power reactor -converts nuclear fission energy into electric power
37.Write note on :Fissile material or fuel
The fissile material or nuclear fuel generally used is 92U235. But
this exists only in a small amount (0.7%) in natural uranium. Natural
uranium is enriched with more number of 92U235 (2 – 4%) and this low
enriched uranium is used as fuel in some reactors.
pressurised heavy water reactors (PHWR) -natural uranium oxide
pressurised light water reactors (PWR)-low enriched uranium
fast breeder test reactor (FBTR)-mixture of the carbides of uranium and plutonium
prototype fast breeder reactor (PFBR) -mixture of oxides of plutonium and uranium
.Kamini - alloy of uranium and aluminium
38.Write note on :Moderator
The function of a moderator is to slow down fast neutrons
produced in the fission process having an average energy of about
2 MeV to thermal neutrons with an average energy of about 0.025 eV,
which are in thermal equilibrium with the moderator. Ordinary water
and heavy water are the commonly used moderators. A good
moderator slows down neutrons by elastic collisions and it does not
remove them by absorption.

39.Write note on :Control rods
The control rods are used to control the chain reaction. They are
very good absorbers of neutrons. The commonly used control rods are
made up of elements like boron or cadmium.In our country, all the power
reactors use boron carbide (B4C), a ceramic material as control rod.
40.Write note on :The cooling system.
The cooling system removes the heat generated in the reactor
core. Ordinary water, heavy water and liquid sodium are the commonly
used coolants. A good coolant must possess large specific heat capacity
and high boiling point.
41.Why liquid sodium used as coolant in fast breeder reactors?
In fast breeder reactors, liquid sodium is used as the coolant. A
high temperature is produced in the reactor core of the fast breeder
reactors. Being a metal substance, liquid sodium is a very good
conductor of heat and it remains in the liquid state for a very high
temperature as its boiling point is about 1000o C.

42.What are Breeder reactors?
The process of producing more fissile material in a reactor than
consumed during the operation of the reactor is called breeding.Such reactors are called breeder reactors.
43.State the Uses of reactors.
(1) Nuclear reactors are mostly aimed at power production,
because of the large amount of energy evolved with fission.
(2) Nuclear reactors are useful to produce radio-isotopes.
(3) Nuclear reactor acts as a source of neutrons, hence used in
the scientific research.
44.Define :Nuclear fusion.
Nuclear fusion is a process in which two or more lighter nuclei
combine to form a heavier nucleus.
Example: 1H3 + 1H2 --> 2He4 + 0n1 + energy
45.What are thermo nuclear reactions?
The fusion process can be carried out only at a extremely high
temperature of the order of 107 K because, only at these very high temperatures the nuclei are able to overcome their mutual repulsion. Therefore before fusion, the lighter nuclei must have their temperature raised by several million degrees. The nuclear fusion reactions are known as thermo-nuclear reactions.
46.What are Cosmic Rays?
Ionising radiation coming from the outer space is the reason for leakage of charges. The ionizing radiation many times stronger than γ-rays entering the earth from all the directions from cosmic or interstellar space is known as cosmic rays. The name, cosmic rays was given by Millikan.
47.What are primary cosmic rays?
The primary cosmic rays are those coming
from outer space and enter the outer boundary of the earth’s
atmosphere. The primary cosmic rays consist of 90% protons, 9%
helium nuclei and remaining heavy nuclei. The energy of the primary
cosmic rays is of the order 108 MeV.
48.What are secondary cosmic rays?
The secondary cosmic rays are produced when primary cosmic
rays interact with gases in the upper layers of the atmosphere. They
are made up of particles like α-particles, protons, electrons, positrons,
mesons, photons, etc. in different proportions.
49.What is Latitude effect of cosmic rays?
The variation of cosmic ray intensity with geomagnetic latitude is known as latitude effect. The experiments to study the variation of cosmic ray intensity (I) with geomagnetic latitude (θ) showed that the intensity is maximum at the poles (θ = 900), minimum at the equator (θ = 0) and constant between latitudes of 420 and 900
50.What is altitude effect of cosmic rays?
The study of variation of cosmic ray intensity (I) with altitude (h) is
known as altitude effect. It is seen that the intensity increases with altitude and reaches a maximum at a height of about 20 km.
51..What is Pair production and annihilation of matter?
The conversion of a photon into an electron−positron pair on its
interaction with the strong electric field surrounding a nucleus is
called pair production.
The converse of pair production in which an electron and positron
combine to produce a photon is known as annihilation of matter.

2009-06-27T05:02:00.001-07:00

7. Dual Nature of Radiation and Matter and Relativity
1.What is Photoelectric effect (or)photoelectric emission?
Photoelectric emission is the phenomena by which a good number
of substances, chiefly metals, emit electrons under the influence of
radiation such as γ rays, X-rays, ultraviolet and even visible light. This
effect was discovered by Heinrich Hertz.
2.Define saturation current.
When the positive potential of anode A is increased, the photoelectric current is also increased, if the positive potential is further increased such that it is large enough to collect all the photo electrons emitted from the cathode plate C,the photoelectric current reaches a certain maximum value and this current is known as saturation current.
3.Define stopping (or) cutoff potential.
If the negative or retarding potential applied to anodeis increased, the photo current decreases and finally becomes zero at a particular value. This minimum negative (retarding) potential given to the anode for which the photo electric current becomes zero is called the cut-off or stopping potential.
4.Define threshold frequency.
Threshold frequency is defined as the minimum frequency of incident radiation below which the photoelectric emission is not possible completely,however high the intensity of incident radiation may be. The threshold frequency is different for different metals.
5.Why photon is considered neither a particle nor a wave?
How photon has dual nature?
Photon is neither a particle nor a wave. In the phenomena like
interference, diffraction, polarisation, the photon behaves like a wave.
In the phenomena like emission, absorption and interaction with matter
(photo electric effect) photon behaves as a particle. Hence light photon
has a dual nature.
6.Define photoelectric work function.
A part of the energy of the photon falling on metal surfaceis used in extracting the electron from the surface of metal, since the electrons in the metal are bound to the nucleus. This energy W spent in releasing the photo electron is known as photoelectric work function of the metal.
7.What is photoelectric cells?State its types.
The photoelectric cell is a device which converts light energy
into electrical energy. The photo electric cells are of three types:
(i) Photo emissive cell (ii) Photo voltaic cell and (iii) Photo conductive cell
8.State four applications of photo electric cells.
(i) Photoelectric cells are used for reproducing sound in
cinematography.
(ii) They are used for controlling the temperature of
furnaces.
(iii) Photoelectric cells are used for automatic switching on
and off the street lights.
(iv) Photoelectric cells are used in the study of temperature
and spectra of stars.
9.How photoelectric cells used in burglar alarm?
In burglar alarm, ultraviolet light is continuously made to fall on the
photo-cell installed at the door-way. A person entering the door
interrupts the beam falling on the photo-cell. The abrupt change in
photocurrent is used to start an electric bell ringing.
10.How photoelectric cells used in fire alarm?
In fire alarm, a number of photo-cells are installed at suitable places in a building. In the event of breaking out of fire, light radiations fall upon the photocell.This completes the electric circuit through an electric bell or a siren which starts operating as a warning signal.

11.State the uses of electron microscope.
(i) It is used in the industry, to study the structure of textile
fibres, surface of metals, composition of paints etc.
(ii) In medicine and biology, it is used to study virus, and
bacteria.
(iii) In Physics, it has been used in the investigation of atomic
structure and structure of crystals in detail.
12.State the Limitations of electron microscope.
An electron microscope is operated only in high vacuum. This
prohibits the use of the microscope to study living organisms which
would evaporate and disintegrate under such conditions.
13.Write note on :Concept of Space
In classical mechanics, motion in absolute space led to two
useful results.
(i) Fixed frame of reference by which the position or motion of
any object in the universe could be measured.
(ii) The geometrical form of an object remains the same irrespective of changes in position or state of motion of the object or observer.

14.Write note on : Concept of time
According to classical mechanics,
(i) The time interval between two events has the same value for all
observers irrespective of their motion.
(ii) If two events are simultaneous for an observer, they are
simultaneous for all observers, irrespective of their position or motion.
This means simultaneity is absolute.
15.What is frame of reference?
A system of co-ordinate axes which defines the position of a
particle in two or three dimensional space is called a frame of reference.
The simplest frame of reference is the Cartesian co-ordinate
system in which the position of a particle is specified by three coordinates x,y and z. There are two types of frames of reference
(i) inertial and (ii) non – inertial frames.
16.Define Inertial (or) unaccelerated frames.
A frame of reference is said to be inertial, when the bodies in
this frame obey Newton’s law of intertia and other laws of Newtonian
mechanics. In this frame, a body remains at rest or in continuous
motion unless acted upon by an external force.
17.Define : Non-inertial (or) accelerated frames
A frame of reference is said to be a non-intertial frame, when a
body not acted upon by an external force, is accelerated. In this frame,
Newton’s laws are not valid.
18.State postulates of special theory of relativity.
The two fundamental postulates of the special theory of relativity
are : (i) The laws of Physics are the same in all inertial frames of
reference. (ii) The velocity of light in free space is a constant in all the
frames of reference.
19.Write note on Length contraction (or) Lorentz-Fitzgerald contraction.
The length of the rod as measured by the observer at rest is lo, and the length of the rod is measured as l by the moving observer. (l < lo).
The length of the rod moving with a velocity v relative to the observer at rest is contracted by a factor.This is known as Lorentz – Fitzgerald contraction.Example : A circular object will appear as an ellipse for a fast moving observer as shown

6.ATOMIC PHYSICS.

2009-06-27T04:57:00.000-07:00

6.ATOMIC PHYSICS.
1.How electric current passes through gases?
Electric current may be passed through a gas if by some mechanism, charged particles are produced in the gas. This can be done
(i) by applying a large potential difference across a gas column at very low pressure and (ii) by allowing X-rays to pass through the gases.
2.Define positive coulumn.
As the pressure is reduced to the order of 10 mm of Hg, the irregular streaks broaden out into a luminous column extending from the anode, almost upto the cathode. This column is known as the positive column.
3.Define Crooke’s dark space.
With further reduction in pressure to around 0.01 mm of Hg, the positive column disappears and Crooke’s dark space fills the whole tube.
4.What are cathode rays?
When the pressure reduced to around 0.01 mm of Hg, the positive column disappears and Crooke’s dark space fills the whole tube.At this stage,the walls of the glass tube fluoresce with green colour. This greenish glow in the final stage of the gaseous discharge is found to be a fluorescence of the glass produced by some invisible rays emanating from the cathode . These rays are called cathode rays and are found to be electrons.
5.State the properties of cathode rays.
(i) They travel in straight lines.
(ii) Cathode rays possess momentum and kinetic energy.
(iii) Cathode rays produce heat, when allowed to fall on matter.
(iv) Cathode rays produce fluorescence when they strike a number
of crystals, minerals and salts.
(v) When cathode rays strike a solid substance of large atomic
weight, X-rays are produced.
(vi) Cathode rays ionize the gas through which they pass.
(vii) Cathode rays affect the photographic plates.
(viii) The cathode rays are deflected from their straight line path
by both electric and magnetic fields. The direction of deflection shows
that they are negatively charged particles.
(ix) Cathode rays travel with a velocity upto (1/10)th of the velocity
of light.
(x) Cathode rays comprises of electrons which are fundamental
constituents of all atoms.
6.State the Properties of Canal rays
(i) They are the streams of positive ions of the gas enclosed in the
discharge tube. The mass of each ion is nearly equal to the mass of the
atom.
(ii) They are deflected by electric and magnetic fields. Their
deflection is opposite to that of cathode rays.
(iii) They travel in straight lines.
(iv) The velocity of canal rays is much smaller than the velocity of
cathode rays.
(v) They affect photographic plates.
(vi) These rays can produce fluorescence.
(vii) They ionize the gas through which they pass.
7.State the principle of Millikan’s oil drop experiment
Millikan’s oil drop method is based on the study of the motion of uncharged oil drop under free fall due to gravity and charged oil drop in a uniform electric field. By adjusting uniform electric field suitably, a charged oil drop can be made to move up or down or even kept balanced in the field of view for sufficiently long time and a series of observations can be made.
8.Define Thomson atom model.
According to Thomson, an atom is a sphere of positive charge having a
radius of the order of 10-10m. The positive charge is uniformly
distributed over the entire sphere and the electrons are embedded in
the sphere of positive charge . The total positive charge inside the atom is equal to the total negative charge carried by the electrons, so that every atom is electrically neutral.
9.State the drawbacks of Thomson,s atom model.
(i) According to electromagnetic theory, the vibrating electron
should radiate energy and the frequency of the emitted spectral line
should be the same as the electron. In the case of hydrogen atom,
Thomson’s model gives only one spectral line of about 1300 Å. But the
experimental observations reveal that hydrogen spectrum consists of
five different series with several lines in each series.
(ii) It could not account for the scattering of α-particles through
large angles.
10.State the observations and conclusions of Rutherford,s atom model.
(i) Most of the α particles either passed straight through the gold
foil or were scattered by only small angles of the order of a few degrees.
This observation led to the conclusion that an atom has a lot of empty space .
(ii) A few α particles were scattered in the backward direction, which led Rutherford to conclude that the whole of the positive charge was concentrated in a tiny space of about 10-14m. This region of the
atom was named as nucleus. Only a small number of particles approaches the nucleus of the atom and they were deflected at large angles.
11.Define :Distance of closest approach
An alpha particle directed towards the centre of the nucleus will move
close upto a distance ro, where its kinetic energy will appear as electrostatic potential energy. After this, the α particle
begins to retrace its path. This distance ro is known as the distance of
the closest approach.
12. State the results of Rutherford alpha scattering experiment.
Based on the results of α-particle scattering experiment,
Rutherford suggested the following.
(i) Atom may be regarded as a sphere of diameter 10-10m, but
whole of the positive charge and almost the entire mass of the atom is
concentrated in a small central core called nucleus having diameter of
about 10-14m
(ii) The electrons in the atom were considered to be distributed
around the nucleus in the empty space of the atom. If the electrons
were at rest, they would be attracted and neutralized by the nucleus.
To overcome this, Rutherford suggested that the electrons are revolving
around the nucleus in circular orbits, so that the centripetal force is
provided by the electrostatic force of attraction between the electron
and the nucleus.
(iii) As the atom is electrically neutral, the total positive charge
of the nucleus is equal to the total negative charge of the electrons in
it.
13.State Bohr,s quantization condition.
An electron cannot revolve round the nucleus in all possible
orbits. The electrons can revolve round the nucleus only in those
allowed or permissible orbits for which the angular momentum of the
electron is an integral multiple of(h/2π) (where h is Planck’s constant =
6.626 × 10-34 Js). These orbits are called stationary orbits or nonradiating orbits and an electron revolving in these orbits does not
radiate any energy.This is called Bohr’s quantization condition.
14.State Bohr,s frequency condition.
An atom radiates energy, only when an electron jumps from a stationary orbit of higher energy to an orbit of lower energy. If the electron jumps from an orbit of energy E2 to an orbit of energy E1, a photon of energy hν = E2 – E1 is emitted. This condition is called Bohr’s frequency condition.

15.Define Lyman series
When the electron jumps from any of the outer orbits to the
first orbit, the spectral lines emitted are in the ultraviolet region of
the spectrum and they are said to form a series called Lyman
series .Here, n1 = 1, n2 = 2,3,4 …
16.Define Balmer series
When the electron jumps from any of the outer orbits to the
second orbit, we get a spectral series called the Balmer series. All the
lines of this series in hydrogen have their wavelength in the visible
region. Here n1=2, n2 = 3,4,5 …
17.Define Paschen series
This series consists of all wavelengths which are emitted when
the electron jumps from outer most orbits to the third orbit. Here n2
= 4,5,6 … and n1 = 3. This series is in the infrared region with the
wave number given by
18.Define Brackett series
The series obtained by the transition of the electron from
n2 = 5, 6... to n1 = 4 is called Brackett series. The wavelengths of these
lines are in the infrared region.
19.Define Pfund series
The lines of the series are obtained when the electron jumps from
any state n2 = 6, 7... to n1=5. This series also lies in the infrared region.
The wave number =
20.Define excitation potential,ionisation potential.
The energy required to raise an atom from its normal state into an excited state is called excitation potential energy of the atom.
The ionisation potential is that accelerating potential which
makes the impinging electron acquire sufficient energy to knock out
an electron from the atom and thereby ionise the atom.
21.Define critical potential.
The excitation potential and ionization potential are called as
the critical potentials of the atom. The critical potential of an atom, is
defined as the minimum potential required to excite a free neutral
atom from its ground state to higher state.
22.What are two main modifications that Sommerfeld introduced in Bohr’s theory?.
(i) According to Sommerfeld, the path of an electron around the
nucleus, in general, is an ellipse with the nucleus at one of its foci.
(ii) The velocity of the electron moving in an elliptical orbit varies
at different parts of the orbit. This causes the relativistic variation in
the mass of the moving electron.
23.What are the drawbacks of Sommerfeld atom model.?
(i) Though Sommerfeld’s modification gave a theoretical
background of the fine structure of spectral lines of hydrogen, it could
not predict the correct number of observed fine structure of these lines.
(ii) It could not explain the distribution and arrangement of
electrons in atoms.
(iii) Sommerfeld’s model was unable to explain the spectra of
alkali metals such as sodium, potassium etc.
(iv) It could not explain Zeeman and Stark effect.
(v) This model does not give any explanation for the intensities of
the spectral lines.
24.What are the basic requirement for the production of X–rays ?
(i) a source of electrons, (ii) effective means of accelerating
the electrons and (iii) a target of suitable material of high atomic weight.
25.What are the characteristics of anode used in x-ray production?
The characteristics of anode used in x-ray production are
(i) high atomic weight – to produce hard X-ray
(ii) high melting point – so that it is not melted due to the
bombardment of fast moving electrons, which cause lot of heat
generation.
(iii) high thermal conductivity – to carry away the heat generated.
26.What are Soft X–rays?
X–rays having wavelength of 4Å or above, have lesser frequency
and hence lesser energy. They are called soft X – rays due to their low
penetrating power. They are produced at comparatively low potential
difference.
27.What are Hard X–rays ?
X–rays having low wavelength of the order of 1Å have high
frequency and hence high energy. Their penetrating power is high,
therefore they are called hard X–rays. They are produced at
comparatively high potential difference.
28.State four Properties of X–rays
(i) X–rays are electromagnetic waves of very short wave length.
They travel in straight lines with the velocity of light. They are invisible
to eyes.
(ii) They undergo reflection, refraction, interference, diffraction
and polarisation.
(iii) They are not deflected by electric and magnetic fields. This
indicates that X-rays do not have charged particles.
(iv) They ionize the gas through which they pass.
(v) They affect photographic plates.
(vi) X–rays can penetrate through the substances which are
opaque to ordinary light e.g. wood, flesh, thick paper, thin sheets of
metals.
(vii) When X–rays fall on certain metals, they liberate photo
electrons (Photo electric effect).
(viii) X-rays have destructive effect on living tissue. When the
human body is exposed to X-rays, it causes redness of the skin, sores
and serious injuries to the tissues and glands. They destroy the white
corpuscles of the blood.
(ix) X–rays do not pass through heavy metals such as lead and
bones. If such objects are placed in their path, they cast their shadow.

29.Why gratings are not used for X-ray diffraction?
Diffraction effects can only be observed if the spacing between the lines ruled on the grating is of the order of magnitude of wavelength of the wave used. Thus, in order to diffract X–rays, grating with much finer rulings, having distance between rulings comparable to the wave length of X–rays are required.
It is impossible to construct a grating of such fine dimensions
artificially.
30.Why crystals are used for X-ray diffraction?
In a crystal, the atoms or molecules are arranged symmetrically in a three dimensional space. Any plane containing an arrangement of atoms is known as lattice plane or cleavage plane. The spacing between the atoms is of the order of 10-10 m, comparable to the wavelength of X-rays. & suggested that the regular arrangement of atoms or molecules in the cleavage planes of a crystal might provide a grating element suitable to diffract X–rays. The crystal might serve as a three dimensional grating, whereas optical grating is a two dimensional one.
31.State Moseley’s law.
Moseley,s law state thatthe frequency of the spectral line in the characteristic X-ray spectrum is directly proportional to the square of the atomic number (Z) of the element considered. This is known as Moseley’s law. i.e ν α Z2 or ν =a(Z −b) where a and b are constants depending upon the particular spectral line.
32.State the applications of Moseley’s law
(i) Any discrepancy in the order of the elements in the periodic table can be removed by Moseley’s law by arranging the elements according to the atomic numbers and not according to the atomic weights.
(ii) Moseley’s law has led to the discovery of new elements like
hafnium (72), technetium (43), rhenium (75) etc.
(iii) This law has been helpful in determining the atomic number
of rare earths, thereby fixing their position in the periodic table.
below:
33.State the Applications of X–rays in Medical field.
(i) X–rays are being widely used for detecting fractures, tumours,
the presence of foreign matter like bullet etc., in the human body.
(ii) X–rays are also used for the diagnosis of tuberculosis, stones
in kidneys, gall bladder etc.
(iii) Many types of skin diseases, malignant sores, cancer and tumours have been cured by controlled exposure of X-rays of suitable quality.
(iv) Hard X–rays are used to destroy tumours very deep inside the
body.
34.State the Industrial applications of X-rays?
(i) X–rays are used to detect the defects or flaws within a material
(ii) X–rays can be used for testing the homogeneity of welded
joints, insulating materials etc.
(iii) X-rays are used to analyse the structure of alloys and the
other composite bodies.
(iv) X–rays are also used to study the structure of materials like
rubber, cellulose, plastic fibres etc.
35.State the Scientific research applications of X-rays?
(i) X–rays are used for studying the structure of crystalline solids
and alloys.
(ii) X–rays are used for the identification of chemical elements
including determination of their atomic numbers.
(iii) X–rays can be used for analyzing the structure of complex
molecules by examining their X–ray diffraction pattern.
36.What is Laser? State its characteristics.
The word ‘Laser’ is an acronym for Light Amplification by Stimulated
Emission of Radiation
Characteristics of laser
The laser beam (i) is monochromatic. (ii) is coherent, with the
waves, all exactly in phase with one another, (iii) does not diverge at
all and (iv) is extremely intense
37.Define normal population.
In a system of thermal equilibrium, the number of atoms in the ground state (N1) is greater than the number of atoms in the excited state (N2). This is called normal population
38.Define stimulated absorption.
Consider a sample of free atoms, some of which are in the ground state with energy E1 and some in the excited energy state with energy E2.
If photons of energy hν = E2-E1 are incident on the sample, the photons can interact with the atoms in the ground state and are taken to excited state. This is called stimulated or induced absorption
39.Define pumping and optical pumping.
The process by which the atoms in the ground state is taken to
the excited state is known as pumping.
I f the atoms are taken to the higher energy levels with the help of light, it is called optical pumping.
40.Define population inversion.
If the atoms in the ground state are pumped to the excited
state by means of external agency, the number of atoms in the excited
state (N2) becomes greater than the number of atoms in the ground state (N1). This is called population inversion.
41. Define metastable state.
The life time of atoms in the excited state is normally 10-8 second. Some of the excited energy levels have greater life times for atoms (10-3s). Such energy levels are called as the metastable states.
42. Define spontaneous emission.
If the excited energy level is an ordinary level, the excited atoms return
to the lower (or) ground energy state immediately without the help of any
external agency. During this transition ,a photon of energy
E2-E1 = hν is emitted. This is called spontaneous emission.
43.Define stimulated emission.
If the excited state is a metastable state, the atoms stay for some
time in these levels. The atoms in such metastable state can be
brought to the lower energy levels with the help of photons of energy
hν = E2 – E1. During this process, a photon of energy E2 – E1 = hν is
emitted. This is known as stimulated emission (or) induced emission.
44.State the Conditions to achieve laser action.
(i) There must be an inverted population i.e. more atoms in the
excited state than in the ground state.
(ii) The excited state must be a metastable state.
(iii) The emitted photons must stimulate further emission. This is
achieved by the use of the reflecting mirrors at the ends of the system.
45.State the Industrial applications of laser
(i) The laser beam is used to drill extremely fine holes in
diamonds, hard sheets etc.,
(ii) They are also used for cutting thick sheets of hard metals
and welding.
(iii) The laser beam is used to vapourize the unwanted material
during the manufacture of electronic circuit on semiconductor chips.
(iv) They can be used to test the quality of the materials.
46.State the Medical applications of laser.
(i) In medicine, micro surgery has become possible due to narrow
angular spread of the laser beam.
(ii) It can be used in the treatment of kidney stone, tumour, in
cutting and sealing the small blood vessels in brain surgery and retina
detachment.
(iii) The laser beams are used in endoscopy.
(iv) It can also be used for the treatment of human and animal
cancer.
47.State the Scientific and Engineering applications of laser.
(i) Since the laser beam can stay on at a single frequency, it can
be modulated to transmit large number of messages at a time in radio,
television and telephone.
(ii) The semiconductor laser is the best light source for optical
fiber communication.
(iii) Narrow angular spread of the laser beam makes it a very
useful tool for microwave communication. Communication with earth
satellites and in rocketry. Laser is also used in accurate range finders
for detecting the targets.
(iv) The earth-moon distance has been measured with the help of
lasers.
(v) It is used in laser Raman Spectroscopy.
(vi) Laser is also used in holography (three dimensional lensless
photography)
(vii) Laser beam can determine precisely the distance, velocity
and direction as well as the size and form of the objects by means of
the reflected signal as in radar.

48. State about Holography.
When an object is photographed by a camera, a two dimensional
image of three dimensional object is obtained. A three dimensional
image of an object can be formed by holography. In ordinary
photography, the amplitude of the light wave is recorded on the
photographic film. In holography, both the phase and amplitude of the
light waves are recorded on the film. The resulting photograph is called
hologram.

Lesson: 5. Electromagnetic waves and Wave Optics.

2009-06-27T04:54:00.000-07:00

Lesson: 5. Electromagnetic waves and Wave Optics.
1.Whar are Electromagnetic waves?
According to Maxwell, an accelerated charge is a source of electromagnetic radiation. In an electromagnetic wave, electric and magnetic field vectors are at right angles to each other and both are at right angles to the direction of propagation. They possess the wave
character and propagate through free space without any material
medium. These waves are transverse in nature.
2.State the Characteristics of electromagnetic waves.
(i) Electromagnetic waves are produced by accelerated charges.
(ii) They do not require any material medium for propagation.
(iii) In an electromagnetic wave, the electric field vectors are at right angles to each other and to the direction of propagation. Hence electromagnetic waves are transverse in nature.
(iv) Variation of maxima and minima in both electric &magnetic fields occur simultaneously.
(v) They travel in vacuum or free space with a velocity
3 × 108 m s−1 given by the relation C =1/ μo εo
(μo – permeability of free space and εo - permittivity of free space)
(vi) The energy in an electromagnetic wave is equally divided
between electric and magnetic field vectors.
(vii) The electromagnetic waves being chargeless, are not deflected
by electric and magnetic fields.
3.State the uses of radio waves.
These waves are used in radio and televisioncommunication systems.
AM band is from 530 kHz to 1710 kHz.
Higher frequencies upto 54 MHz are used for short waves bands.
Television waves range from 54 MHz to 890 MHz.
FM band is from 88 MHz to 108 MHz.
Cellular phones use radio waves in ultra high frequency (UHF) band.

4.State the uses of micro waves.
Due to their short wavelengths, they are used in radar communication system. Microwave ovens are an interesting domestic application of these waves.
5.State the uses of infra red waves.
Infrared lamps are used in physiotherapy.
Infrared photographs are used in weather forecasting.
As infrared radiations are not absorbed by air, thick fog, mist etc, they are used to take photograph of long distance objects.
Infra red absorption spectrum is used to study the molecular structure.
6.State the uses Ultra−violet radiations
(i) They are used to destroy the bacteria and for sterilizing
surgical instruments.
(ii) These radiations are used in detection of forged documents,
finger prints in forensic laboratories.
(iii) They are used to preserve the food items.
(iv) They help to find the structure of atoms.
7.State the use X rays & γ−rays
X rays
(i) X rays are used as a diagonistic tool in medicine.
(ii) It is used to study the crystal structure in solids.
γ−rays
Study of γ rays gives useful information about the
nuclear structure and it is used for treatment of cancer.
8.Define:Emission spectra
When the light emitted directly from a source is examined with
a spectrometer, the emission spectrum is obtained. Every source has
its own characteristic emission spectrum.
9. Define Continuous emission spectrum
· It consists of unbroken luminous bands of all wavelengths
containing all the colours from violet to red. These spectra depend only
on the temperature of the source and is independent of the
characteristic of the source.
· Incandescent solids, liquids, Carbon arc, electric filament lamps
etc, give continuous spectra.
10. Define Line emission spectrum
Line spectra are sharp lines of definite wavelengths. It is the
characteristic of the emitting substance. It is used to identify the gas.
Atoms in the gaseous state, i.e. free excited atoms emit line spectrum. The substance in atomic state such as sodium in sodium vapour lamp, mercury in mercury vapour lamp and gases in discharge tube give line spectra
11. Define Band emission Spectrum
It consists of a number of bright bands with a sharp edge at one end but fading out at the other end.
Band spectra are obtained from molecules. It is the characteristic of the molecule. Calcium or Barium salts in a bunsen flame and gases like carbon−di−oxide, ammonia and nitrogen in molecular state in the discharge tube give band spectra.
When the bands are examined with high resolving power spectrometer,each band is found to be made of a large number of fine lines, very close to each other at the sharp edge but spaced out at the other end. Using band spectra the molecular structure of the substance can be studied.
12. Define: Absorption Spectra
When the light emitted from a source is made to pass through an
absorbing material and then examined with a spectrometer, the
obtained spectrum is called absorption spectrum. It is the
characteristic of the absorbing substance.
Absorption spectra is also of three types
1. continuous absorption spectrum
2. line absorption spectrum and
3. band absorption spectrum
13 Define: Continuous absorption spectrum
A pure green glass plate when placed in the path of white light,
absorbs everything except green and gives continuous absorption
spectrum.
14. Define: Line absorption spectrum
When light from the carbon arc is made to pass through sodium
vapour and then examined by a spectrometer, a continuous spectrum
of carbon arc with two dark lines in the yellow region is obtained
15. Define: Band absorption spectrum
If white light is allowed to pass through iodine vapour or dilute
solution of blood or chlorophyll or through certain solutions of organic
and inorganic compounds, dark bands on continuous bright background are obtained. The band absorption spectra are used for making dyes.
16.What are Fraunhofer lines?
If the solar spectrum is closely examined, it is found that it
consists of large number of dark lines. These dark lines in the solar
spectrum are called Fraunhofer lines. Solar spectrum is an example of
line absorption spectrum.
By comparing the absorption spectra of various substances with
the Fraunhofer lines in the solar spectrum, the elements present in the
sun’s atmosphere have been identified.
17.What is Fluorescence?
When an atomic or molecular system is excited into higher energy
state by absorption of energy, it returns back to lower energy state in
a time less than 10−5 second and the system is found to glow brightly
by emitting radiation of longer wavelength.
When ultra violet light is incident on certain substances, they
emit visible light.
It may be noted that fluorescence exists as long as the fluorescing
substance remain exposed to incident ultraviolet light and re-emission
of light stops as soon as incident light is cut off.
18.What is Phosphorescence?
There are some substances in which the molecules are excited by
the absorption of incident ultraviolet light, and they do not return
immediately to their original state. The emission of light continues even
after the exciting radiation is removed. This type of delayed
fluorescence is called phosphorescence.
19.What are two possible modes of propagation of energy?
The two possible modes of propagation of energy from one place to another
(i) by stream of material particles moving with a finite velocity
(ii) by wave motion, wherein the matter through
which the wave propagates does not move along the direction of the
wave.
20.Define :Scattering of light
Lord Rayleigh was the first to deal with scattering of light by air
molecules. The scattering of sunlight by the molecules of the gases in
Earth’s atmosphere is called Rayleigh scattering.
The basic process in scattering is absorption of light by the
molecules followed by its re-radiation in different directions.
21.State Rayleigh scattering law.
The amount of scattering is inversely proportional to the fourth
power of the wavelength. This is known as Rayleigh scattering law.
22.Why sky appears blue at noon?
The shorter wavelengths are scattered much more than the
longer wavelengths. The blue appearance of sky is due to scattering of
sunlight by the atmosphere. According to Rayleigh’s scattering law,
blue light is scattered to a greater extent than red light. This scattered
radiation causes the sky to appear blue.
23.Why sun appears red at sunset/sunrise?
At sunrise and sunset the rays from the sun have to travel a larger part of the atmosphere than at noon. Therefore most of the blue light is scattered away and only the red light which is least scattered reaches the observer. Hence, sun appears reddish at sunrise and sunset.
24.What is Tyndal scattering?
When light passes through a colloidal solution its path is visible inside the solution. This is because, the light is scattered by the particles of solution. The scattering of light by the colloidal particles is called Tyndal scattering.
25.What is Raman effect?
In 1928, Sir C.V. Raman discovered experimentally, that the
monochromatic light is scattered when it is allowed to pass through a
substance. The scattered light contains some additional frequencies
other than that of incident frequency. This is known as Raman effect.
The lines having frequencies lower than the incident frequency are called Stoke’s lines and the lines having frequencies higher than the incident frequency are called Anti−stokes lines.
26.Define :stokes lines.
If a photon strikes an atom or a molecule in a liquid, part of
the energy of the incident photon may be used to excite the atom of the
liquid and the rest is scattered. The spectral line will have lower
frequency and it is called stokes line.
27.Define: Antistokes lines.
If a photon strikes an atom or a molecule in a liquid, which is in
an excited state, the scattered photon gains energy. The spectral line will
have higher frequency and it is called Anti−stoke’s line.
28,State the Applications of Raman Spectrum
(i) It is widely used in almost all branches of science.
(ii) Raman Spectra of different substances enable to classify them
according to their molecular structure.
(iii) In industry, Raman Spectroscopy is being applied to study the
properties of materials.
(iv) It is used to analyse the chemical constitution.
29.Define: Wavefront.
The surface which envelopes the particles that are in the same state of vibration is known as a wave front. The wave front at any instant is defined as the locus of all the particles of the medium which are in the same state of
vibration.
A point source of light at a finite distance in an isotropic medium
emits a spherical wave front. A point source of light in an
isotropic medium at infinite distance will give rise to plane wavefront
A linear source of light such as a slit illuminated by a lamp,
will give rise to cylindrical wavefront
30.State: Huygen’s principle
Huygen’s principle states that, (i) every point on a given wave front
may be considered as a source of secondary wavelets which spread out
with the speed of light in that medium and (ii) the new wavefront is the
forward envelope of the secondary wavelets at that instant.
31.State the conditions for total internal reflection.
For total internal reflection to take place (i) light must travel
from a denser medium to a rarer medium and (ii) the angle of incidence
inside the denser medium must be greater than the critical angle. i.e i > C.
32.State the superposition principle.
When two or more waves simultaneously pass through the same
medium, The resultant displacement of any particle is the vector addition of the displacements due to the individual waves. This is known as principle of superposition. Y = Y + Y
33.What are Coherent sources?
Two sources are said to be coherent if they emit light waves of the
same wave length and start with same phase or have a constant phase
difference.
34.Is two independent sources be coherent?Discuss.
Two independent monochromatic sources, emit waves of same
wave length. But the waves are not in phase. So they are not coherent.
This is because, atoms cannot emit light waves in same phase and
these sources are said to be incoherent sources.
35.Define constructive interference.
At points where the crest of one wave meets the crest of the other wave or the trough of one wave meets the trough of the other wave, the waves are in phase, the displacement is maximum and these points appear bright. This type of interference is said to be constructive interference.
36.Define destructive interference.
At points where the crest of one wave meets the trough of the other wave, the waves are in opposite phase, the displacement is minimum and these points appear dark. This type of interference is said to be destructive interference.

37.State the conditions for the formation of sustained interference.
The conditions for the formation of sustained interference may be stated as :
(i) The two sources should be coherent
(ii) Two sources should be very narrow
(iii) The sources should lie very close to each other to form
distinct and broad fringes.
38.Define: Band width.
The distance between any two consecutive bright or dark bands
is called bandwidth.
Bandwitdth, β =D λ/d
39.State the Condition for obtaining clear and broad interference bands
Condition for obtaining clear and broad interference bands
(i) The screen should be as far away from the source as possible.
(ii) The wavelength of light used must be larger.
(iii) The two coherent sources must be as close as possible.
40.What are Newton’s rings?
When a plano convex lens of long focal length is placed over an optically plane glass plate, a thin air film with varying thickness is enclosed between them. The thickness of the air film is zero at the point of contact and gradually increases outwards from the point of contact. When the air film is illuminated by
monochromatic light normally, alternate bright and dark concentric
circular rings are formed with dark spot at the centre. These rings are
known as Newton’s rings.
41.Why the central ring of Newton’s rings appears dark?
The thickness of the air film at the point of contact of lens L with
glass plate P is zero. Hence, there is no path difference between the
interfering waves. So, it should appear bright. But the wave reflected
from the denser glass plate has suffered a phase change of π while the
wave reflected at the spherical surface of the lens has not suffered any
phase change. Hence the point O appears dark. Around the point of
contact alternate bright and dark rings are formed.
42.Define diffraction:Why sound is more pronounced than light?
The bending of waves around the edges of an obstacle is called diffraction.
The sound waves have a greater wavelength, the diffraction effects are
pronounced. As the wavelength of light is very small, compared to that
of sound wave and even tiny obstacles have large size, compared to the
wavelength of light waves, diffraction effects of light are very small.
43.Differentiate: Fresnel and Fraunhofer diffraction
In the Fresnel diffraction, the source and the screen are at finite distances from the obstacle producing diffraction. In such a case the wave front
undergoing diffraction is either spherical or cylindrical.No convex lens used.
In the Fraunhofer diffraction, the source and the screen are at infinite
distances from the obstacle producing diffraction. Hence in this case
the wavefront undergoing diffraction is plane. The diffracted rays are brought to focus with the help of a convex lens.
44.State the difference between interference and diffraction

Interference

Diffraction

1. It is due to the superposition of
secondary wavelets from two
different wavefronts produced
by two coherent sources
It is due to the superposition
of secondary wavelets emitted
from various points of the
same wave front.

2. Fringes are equally spaced
Fringes are unequally spaced
3. Bright fringes are of same
intensity

Intensity falls rapidly

4. Comparing with diffraction, it
has large number of fringes

It has less number of fringes.

45.Define: Polarisation.
The vibrations of unpolarised ordinary light are restricted to only one plane parallel to the axis of the crystal, the phenomenon of restricting the
vibrations into a particular plane is known as polarisation.
46. Plane of vibration and plane of polarisation
The plane containing the optic axis in which the vibrations occur
is known as plane of vibration. The plane which is at right angles to
the plane of vibration and which contains the direction of propagation
of the polarised light is known as the plane of polarisation. Plane of
polarisation does not contain vibrations in it.
47.What is a polarizer and analyzer?
A device which produces plane polarised light is called a polariser.
A device which is used to examine, whether light is plane polarised or not
is an analyser. A polariser can serve as an analyser and vice versa.
48.What is the test for polarized and unpolarised light?
If the intensity of light from polarizer varies between maximum and zero, when the analyser is rotated through 90o, then the incident light is plane polarised;
If the intensity of light varies between maximum and minimum (not zero), when the analyser is rotated through 90o, then the incident light is partially
plane polarised.
49.State Brewsters law.
The tangent of the polarising angle is numerically equal to the refractive index of the medium. tan ip = μ
50.What is Double refraction.
Bartholinus discovered that when a ray of unpolarised light is
incident on a calcite crystal, two refracted rays are produced. This
phenomenon is called double refraction.
51.What is optic axis?state its types.
Inside the crystal there is a particular direction in which both the
rays travel with same velocity. This direction is called optic axis.
Crystals like calcite, quartz, ice and tourmaline having only one
optic axis are called uniaxial crystals.
Crystals like mica, topaz, selenite and aragonite having two optic
axes are called biaxial crystals.
53.State the Uses of Polaroid.
1. Polaroids are used in the laboratory to produce and analyse plane
polarised light.
2. Polaroids are widely used as polarising sun glasses.
3. They are used to eliminate the head light glare in motor cars.
4. They are used to improve colour contrasts in old oil paintings.
5. Polaroid films are used to produce three – dimensional moving
pictures.
6. They are used as glass windows in trains and aeroplanes to control
the intensity of light. In aeroplane one polaroid is fixed outside the
window while the other is fitted inside which can be rotated. The
intensity of light can be adjusted by rotating the inner polaroid.
7. Aerial pictures may be taken from slightly different angles and
when viewed through polaroids give a better perception of depth.
8. In calculators and watches, letters and numbers are formed by
liquid crystal display (LCD) through polarisation of light.
9. Polarisation is also used to study size and shape of molecules.
54.Define: Optical activity
When a plane polarised light is made to pass through certain
substances, the plane of polarisation of the emergent light is not the
same as that of incident light, but it has been rotated through some
angle. This phenomenon is known as optical activity. The substances
which rotate the plane of polarisation are said to be optically active.
Examples : quartz, sugar crystals, turpentine oil, sodium chloride etc.
55.Define the types of optically active substances.
Optically active substances are of two types, (i) Dextro−rotatory
(right handed) which rotate the plane of polarisation in the clock wise
direction on looking towards the source. (ii) Laevo – rotatory (left
handed) which rotate the plane of polarisation in the anti clockwise
direction on looking towards the source.
56.State the factors of optical rotation.
The amount of optical rotation depends on :
(i) thickness of crystal
(ii) density of the crystal or concentration in the case of solutions.
(iii) wavelength of light used
(iv) the temperature of the solutions.

57.Define :Specific rotation
Specific rotation for a given wavelength of light at a given
temperature is defined as the rotation produced by one-decimeter
length of the liquid column containing 1 gram of the active material in
1cc of the solution.
If θ is the angle of rotation produced by l decimeter length of a
solution of concentration C in gram per cc, then the specific rotation
S at a given wavelength λ for a given temperature t is given by
S = θ/ l c .

4. Electromagnetic Induction and Alternating Current

2009-06-27T04:52:00.000-07:00

4. Electromagnetic Induction and Alternating Current

1.Define “magnetic flux”.
The magnetic flux (φ) linked with a surface held in a magnetic field (B) is defined as the number of magnetic lines of force crossing a closed area (A). If θ is the angle between the direction of the field and normal to the area, Then φ = B . A φ = BA cos θ.
2.Define :Electromagnetic induction.
Whenever there is a change in the magnetic flux linked with a closed circuit an emf is produced. This emf is known as the induced emf and the current that flows in the closed circuit is called induced current.
The phenomenon of producing an induced emf due to the changes in the magnetic flux associated with a closed circuit is known as
electromagnetic induction.
3.State Faraday’s first law of electromagnetic induction.
Whenever the amount of magnetic flux linked with a closed circuit changes, an emf is induced in the circuit. The induced emf lasts
so long as the change in magnetic flux continues.

4.State Faraday’s second law of electromagnetic induction.
The magnitude of emf induced in a closed circuit is directly
proportional to the rate of change of magnetic flux linked with the
circuit.
Let φ1 be the magnetic flux linked with the coil initially and φ2 be
the magnetic flux linked with the coil after a time t. Then
Rate of change of magnetic flux = (φ2 − φ1)/t
According to Faraday’s second law, the magnitude of induced
emf is, e α = (φ2 − φ1)/t
5.State :Lenz’s law
The Russian scientist H.F. Lenz in 1835 discovered a simple law giving the direction of the induced current produced in a circuit. Lenz’s law states that the induced current produced in a circuit always flows in such a direction that it opposes the change or cause that produces it.
6. State Fleming’s right hand rule
The forefinger, the middle finger and the thumb of the right hand are held in the three mutually perpendicular directions. If the forefinger points along the direction of the magnetic field and the thumb is along
the direction of motion of the conductor, then the middle finger points
in the direction of the induced current. This rule is also called
generator rule.
7.Define :Self Induction
The property of a coil which enables to produce an opposing induced emf in it when the current in the coil changes is called self induction.
8.Define : Coefficient of self induction
The coefficient of self induction of a coil is numerically equal to
the opposing emf induced in the coil when the rate of change of current
through the coil is unity. The unit of self inductance is henry (H).
9.Define :One henry.
One henry is defined as the self-inductance of a coil in which a
change in current of one ampere per second produces an opposing emf
of one volt.
One henry is defined as the coefficient of mutual induction
between a pair of coils when a change of current of one ampere per
second in one coil produces an induced emf of one volt in the other coil.
10.Define :Mutual induction.
Whenever there is a change in the magnetic flux linked with a coil, there is also a change of flux linked with the neighbouring coil, producing an induced emf in the second coil. This phenomenon of producing an induced emf in a coil due to the change in current in the other coil is known as mutual induction.

11.Define:Coefficient of mutual induction.
The coefficient of mutual induction of two coils is numerically equal to the emf induced in one coil when the rate of change of current through the other coil is unity. The unit of coefficient of mutual induction is henry.
12.State the factors of coefficient of mutual induction between pair of coils depends?
The coefficient of mutual induction between a pair of coils
depends on the following factors:
(i) Size and shape of the coils, number of turns and permeability
of material on which the coils are wound.
(ii) proximity of the coils
13.State the methods of producing induced emf
The induced emf is given by the expression e = –d φ/ dt
=d (NBA cos θ)/dt Hence, the induced emf can be produced by changing
(i) the magnetic induction (B)
(ii) area enclosed by the coil (A) and
(iii) the orientation of the coil (θ) with respect to the magnetic field.
14.What is polyphase generator/alternator.
A single phase a.c. generator or alternator has only one armature
winding. If a number of armature windings are used in the alternator
it is known as polyphase alternator. It produces voltage waves equal to
the number of windings or phases
15.What is Eddy currents?
Foucault in the year 1895 observed that “When a mass of metal moves in a magnetic field or when the magnetic field through a stationary mass of metal is altered, induced current is produced in the metal. This induced current flows in the metal in the form of closed loops resembling ‘eddies’ or whirl pool. Hence this current is called eddy current”. The direction of the eddy current is given by Lenz’s law.
16.How Eddy current appliedin Dead beat galvanometer?
When current is passed through a galvanometer, the coil
oscillates about its mean position before it comes to rest. To bring the
coil to rest immediately, the coil is wound on a metallic frame. Now,
when the coil oscillates, eddy currents are set up in the metallic frame,
which opposes further oscillations of the coil. This inturn enables the
coil to attain its equilibrium position almost instantly. Since the
oscillations of the coil die out instantaneously, the galvanometer is
called dead beat galvanometer.

17.How Eddy current applied in Induction furnace?
In an induction furnace, high temperature is produced by
generating eddy currents. The material to be melted is placed in a
varying magnetic field of high frequency. Hence a strong eddy current
is developed inside the metal. Due to the heating effect of the current,
the metal melts.
18.How Eddy current applied in Induction motors?
Eddy currents are produced in a metallic cylinder called rotor,
when it is placed in a rotating magnetic field. The eddy current initially
tries to decrease the relative motion between the cylinder and the
rotating magnetic field. As the magnetic field continues to rotate, the
metallic cylinder is set into rotation. These motors are used in fans.
19.How Eddy current applied in Electro magnetic brakes?
A metallic drum is coupled to the wheels of a train. The drum
rotates along with the wheel when the train is in motion.When the
brake is applied, a strong magnetic field is developed and hence, eddy
currents are produced in the drum which oppose the motion of the
drum. Hence, the train comes to rest.
20.How Eddy current appliedin Speedometer?
In a speedometer, a magnet rotates according to the speed of the
vehicle. The magnet rotates inside an aluminium cylinder (drum) which
is held in position with the help of hair springs. Eddy currents are
produced in the drum due to the rotation of the magnet and it opposes
the motion of the rotating magnet. The drum inturn experiences a
torque and gets deflected through a certain angle depending on the
speed of the vehicle. A pointer attached to the drum moves over a
calibrated scale which indicates the speed of the vehicle.
21.What is a transformer?
Transformer is an electrical device used for converting low alternating
voltage into high alternating voltage and vice versa. It transfers
electric power from one circuit to another. The transformer is based on
the principle of electromagnetic induction.
22.What is transformer ratio (or) turns ratio?
E s / E P = N s/ N P = I P/I s = k
where k is called transformer ratio.For step up transformer k > 1 and
for step down transformer k <> Ep implying that Is < Ip. Thus a step up transformer increases the voltage by decreasing the current, a step down transformer decreases the voltage by increasing the current.

23. Define Efficiency of a transformer.
Efficiency of a transformer is defined as the ratio of output power
to the input power.η =output power/input power
E s I s = E P I P
The efficiency η = 1 (ie. 100%), only for an ideal transformer
where there is no power loss. But practically there are numerous
factors leading to energy loss in a transformer and hence the efficiency
is always less than one.
24.Define Hysteresis loss in a transformer.
The repeated magnetisation and demagnetisation of the iron core
caused by the alternating input current, produces loss in energy called
hysterisis loss.
This loss can be minimised by using a core with a
material having the least hysterisis loss. Alloys like mumetal and
silicon steel are used to reduce hysterisis loss.
25.Define Copper loss in a transformer.
The current flowing through the primary and secondary windings
lead to Joule heating effect. Hence some energy is lost in the form of
heat. Thick wires with considerably low resistance are used to minimise
this loss.
26.Define Eddy current loss in a transformer.
Eddy current loss (Iron loss)
The varying magnetic flux produces eddy current in the core. This leads to the wastage of energy in the form of heat. This loss is minimised by using a laminated core made of stelloy, an alloy of steel.
27.Define Flux loss in a transformer.
The flux produced in the primary coil is not completely linked with the secondary coil due to leakage. This results in the loss of energy.
This loss can be minimised by using a shell type core. In addition to the above losses, due to the vibration of the core, sound is produced, which causes a loss in the energy.
28.Define RMS value of a.c.
The rms value of alternating current is defined as that value of the
steady current, which when passed through a resistor for a given time,
will generate the same amount of heat as generated by an alternating
current when passed through the same resistor for the same time.
The rms value is also called effective value of an a.c. and is
denoted by Irms or Ieff.

29.Define Inductive reactance & Capacitive reactance.
XL = ωL = 2πν L, where ν is the frequency of the a.c. supply
For d.c. ν = 0; XL = 0
1/ωC = XC is the resistance offered by the capacitor. It is called
capacitive reactance. Its unit is ohm .
30.Capacitor allows a.c. but not d.c. Why?
Capacitor offers infinite resistance to d.c. For an a.c. the
capacitive reactance varies inversely as the frequency of a.c. and also
inversely as the capacitance of the capacitor.
31.Define Resonant frequency of the circuit.
The particular frequency νo at which the impedance of the circuit
becomes minimum and therefore the current becomes maximum is
called Resonant frequency of the circuit. Such a circuit which admits
maximum current is called series resonant circuit or acceptor circuit
32.What is an acceptor circuit?
The series resonant circuit is often called an ‘acceptor’ circuit. By
offering minimum impedance to current at the resonant frequency it is
able to select or accept most readily this particular frequency among
many frequencies. In radio receivers the resonant frequency of the circuit is tuned to the frequency of the signal desired to be detected. This is usually done by varying the capacitance of a capacitor.
33.Define Q-factor (or) quality factor.
The selectivity or sharpness of a resonant circuit is measured by
the quality factor or Q factor. In other words it refers to the sharpness
of tuning at resonance.
The Q factor of a series resonant circuit is defined as the ratio of
the voltage across a coil or capacitor to the applied voltage.
Q =voltage across L or C/applied voltage
34.What is a Choke coil ?
A choke coil is an inductance coil of very small resistance used
for controlling current in an a.c. circuit. If a resistance is used to
control current, there is wastage of power due to Joule heating effect
in the resistance. On the other hand there is no dissipation of power
when a current flows through a pure inductor.
35.What are types of choke coil?.
Chokes used in low frequency a.c. circuit have an iron core so
that the inductance may be high. These chokes are known as audio –
frequency (A.F) chokes. For radio frequencies, air chokes are used since
a low inductance is sufficient. These are called radio frequency (R. F)
or high frequency (H.F) chokes and are used in wireless receiver
circuits

3. EFFECTS OF ELECTRIC CURRENT

2009-06-27T04:48:00.000-07:00

3. EFFECTS OF ELECTRIC CURRENT

1.STATE JOULE’S LAW OF HEATING EFFECT.
Joule’s law: H = VIt . For a resistance R, H = I2Rt . and H =(V2/R) t .
The heat produced is (i) directly proportional to the square of the
current for a given R (ii) directly proportional to resistance R for a given
I and (iii) directly proportional to the time of passage of current. Also
the heat produced is inversely proportional to resistance R for a given V.
2.What is Nichrome?Why is it used as heating element?
Nichrome which is an alloy of nickel and chromium is used as the heating element for the following reasons. (1) It has high specific resistance
(2) It has high melting point (3) It is not easily oxidized
3.Write note on fuse wire.
Fuse wire is an alloy of lead 37% and tin 63%. It is connected in series in an electric circuit. It has high resistance and low melting point. When large current flows through a circuit due to short circuiting, the fuse wire melts due to heating and hence the circuit becomes open. Therefore, the electric appliances are saved from damage.
4.State Seebeck effect
In 1821, German Physicist Thomas Johann Seebeck discovered that in a circuit consisting of two dissimilar metals like iron and copper, an emf is developed when the junctions are maintained at different temperatures.
Two dissimilar metals connected to form two junctions is called
thermocouple. The emf developed in the circuit is thermo electric emf.
The current through the circuit is called thermoelectric current. This
effect is called thermoelectric effect or Seebeck effect
5.Define Neutral and Inversion temperature
Keeping the temperature of the cold junction constant, the temperature of the hot junction is gradually increased ,the thermo emf rises to a maximum at a temperature (θn) called neutral temperature.
Beyond neutral temperature if we increase the temperature of hot junction the thermo emf gradually decreases and eventually becomes zero at a particular temperature (θi) called temperature of inversion
6. State Peltier effect
In 1834, a French scientist Peltier discovered that when electric
current is passed through a circuit consisting of two dissimilar metals,
heat is evolved at one junction and absorbed at the other junction. This
is called Peltier effect.

7.Define Peltier Co-efficient .
The amount of heat energy absorbed or evolved at one of the
junctions of a thermocouple when one ampere current flows for one
second (one coulomb) is called Peltier coefficient. It is denoted by π. Its
unit is volt. If H is the quantity of heat absorbed or evolved at one
junction then H = π It
8.Define :Thomson effect.
Thomson suggested that when a current flows through unequally
heated conductors, heat energy is absorbed or evolved throughout the
body of the metal.
9.Define :Thomson coefficient .
The amount of heat energy absorbed or evolved when one ampere
current flows for one second (one coulomb) in a metal between two
points which differ in temperature by 1oC is called Thomson coefficient.
It is denoted by σ. Its unit is volt per oC.
10.State Maxwells’s right hand cork screw rule
If a right handed cork screw is rotated to advance along the
direction of the current through a conductor, then the direction of
rotation of the screw gives the direction of the magnetic lines of force
around the conductor.
11.State Biot – Savart Law.
Biot and Savart conducted many experiments to determine the
factors on which the magnetic field due to current in a conductor
depends. i) directly proportional to the current (I)
(ii) directly proportional to the length of the element (dl )
(iii) directly proportional to the sine of the angle between dl and
the line joining element dl and the point P (sin θ)
(iv) inversely proportional to the square of the distance of the
point from the element ( 1/r2)
dB =(μ/4π) (Idlsin θ/r2)
12.State the principle of tangent galvanometer.
Tangent galvanometer is a device used for measuring current. It works on the principle of tangent law. A magnetic needle suspended at a point where there are two crossed fields at right angles to each other will come to rest in the direction of the resultant of the two fields.
13.State Ampere’s Circuital Law
∫BL = μoIo . ∫B.dl = μoIo ...
The line integral ∫B.dl for a closed curve is equal to μo times
the net current Io through the area bounded by the curve.
14. State Right hand palm rule
The coil is held in the right hand so that the fingers point in the direction of the current in the windings. The extended thumb, points in the direction
of the magnetic field.

15.State End rule:
When looked from one end, if the current through the solenoid is along
clockwise direction the nearer end corresponds to south pole
and the other end is north pole.
When looked from one end, if the current through the solenoid is
along anti-clock wise direction, the nearer end corresponds to north
pole and the other end is south pole .
16. Define Magnetic Lorentz force
The force experienced by a moving charge placed in uniform magnetic field depends (i)the force is proportional to the magnitude of the charge (q),
(ii) the force is proportional to the magnetic induction (B), (iii) the force is proportional to the speed of the charge (v) : F = Bqv sin θ
17.State the principle of Cyclotron.
Cyclotron works on the principle that a charged particle moving
normal to a magnetic field experiences magnetic lorentz force due to
which the particle moves in a circular path.

18.State the Limitations of cyclotron.
(i) Maintaining a uniform magnetic field over a large area of the
Dees is difficult. (ii) At high velocities, relativistic variation of mass of the particle upsets the resonance condition. (iii) At high frequencies, relativistic variation of mass of the electron is appreciable and hence electrons cannot be accelerated by cyclotron.
19.State Fleming’s Left Hand Rule.
The forefinger, the middle finger and the thumb of the left hand are stretched in mutually perpendicular directions. If the forefinger points in the direction of the magnetic field, the middle finger points in the direction of the current, then the thumb points in the direction of the force on the conductor.
20.Define one ampere.
Ampere is defined as that constant current which when flowing through two parallel infinitely long straight conductors of negligible cross section and placed in air or vacuum at a distance of one metre apart, experience a force of
2 × 10-7 newton per unit length of the conductor.
21.Define current sensitivity of a galvanometer.
The current sensitivity of a galvanometer is defined as the
deflection produced when unit current passes through the
galvanometer. A galvanometer is said to be sensitive if it produces large
deflection for a small current. In a galvanometer, I =(C/nBA)/θ
Current sensitivity (θ/ I) =(nBA /C)
22.How will you increase current sensitivity of a galvanometer.?
The current sensitivity of a galvanometer can be increased by
(i) increasing the number of turns (ii) increasing the magnetic induction
(iii) increasing the area of the coil (iv) decreasing the couple per unit twist of the suspension wire.

23.Define: Voltage sensitivity of a galvanometer
The voltage sensitivity of a galvanometer is defined as the
deflection per unit voltage. Voltage sensitivity(θ/V) = (θ/IG) = (nBA/CG)
where G is the galvanometer resistance.
24. Increasing the current sensitivity does not necessarily, increase the voltage sensitivity . Why?
When the number of turns (n) is doubled, current sensitivity is also doubled. But increasing the number of turns correspondingly increases the resistance (G). Hence voltage sensitivity remains unchanged.
25.How will you convert galvanometer into an ammeter & voltmeter?
Agalvanometer is converted into an ammeter by connecting a low resistance in parallel with it.
A galvanometer can be converted into a voltmeter by connecting a high resistance in series with it.
26.Define the magnetic moment of a current loop
The magnetic moment of a current loop is defined as the product
of the current and the loop area. Its direction is perpendicular to the
plane of the loop. M = IA

2. CURRENT ELECTRICITY

2009-06-27T04:44:00.000-07:00

2. CURRENT ELECTRICITY
1.DEFINE “CURRENT ELECTRICITY”.
The branch of Physics which deals with the study of motion of
electric charges is called current electricity.
2.DEFINE “EMF” (OR) “ELECTRO MOTIVE FORCE”
The external energy necessary to drive the free
electrons in a definite direction is called electromotive force (emf).
3.DEFINE ELECTRIC CURRENT.WRITE UNIT,EXPRESSION,QTY.
The current is defined as the rate of flow of charges across any
cross sectional area of a conductor. If a net charge q passes through
any cross section of a conductor in time t, then the current I = q / t,
where q is in coulomb and t is in second.
The current I is expressed in ampere.Current is a scalar quantity.
4.DEFINE “DRIFT VELOCITY”.WRITE EXPRESSION.
Drift velocity is defined as the velocity with which free electrons
get drifted towards the positive terminal, when an electric field is
applied. vd =aτ
5.DEFINE MOBILITY. WRITR EXPRESSION.
The mobility is defined as the drift velocity acquired per unit electric field. μ = Vd / E. It takes the unit m2V–1s–1.
6.DEFINE “CURRENT DENSITY”. WRITE EXPRESSION,UNIT,QTY.
Current density at a point is defined as the quantity of charge
passing per unit time through unit area, taken perpendicular to the
direction of flow of charge at that point.
The current density J for a current I flowing across a conductor
having an area of cross section A is J =(q/t) /A = I/ A
Current density is a vector quantity. It is expressed in A m–2
7.STATE OHM’S LAW.
Ohm’s law states that, at a constant temperature, the steady
current flowing through a conductor is directly proportional to the
potential difference between the two ends of the conductor.
(i.e) I α V (or)V = IR .
8. DEFINE RESISTANCE OF A CONDUCTOR.
Resistance of a conductor is defined as the ratio of potential difference across the conductor to the current flowing through it. R =V/I
The unit of resistance is ohm (Ω)
9.DEFINE ELECTRICAL RESISTIVITY.
The electrical resistivity of a material is defined as the resistance offered to current flow by a conductor of unit length having unit area of cross section ρ. =R.A/L.The unit of ρ is ohm−m (Ω m).
10.DEFINE “CONDUCTANCE” AND CONDUCTIVITY”.
The reciprocal of resistance is conductance. ρ. = 1/R.
Its unit is mho (Ω–1).
The reciprocal of electrical resistivity, is called electrical
conductivity, σ = 1/ρ. The unit of conductivity is mho m-1 (Ω–1 m–1)
11.DEFINE CONDUCTORS BASED ON RESISTIVITY.
The resistivity of a material is the characteristic of that particular
material. The materials can be broadly classified into conductors and
insulators. The metals and alloys which have low resistivity of the order
of 10−6 – 10−8 Ω m are good conductors of electricity. They carry
current without appreciable loss of energy. Example : silver,
aluminium, copper, iron, tungsten, nichrome, manganin, constantan.
12.DEFINE INSULATORS (OR) NON-CONDUCTORS BASED ON RESISTIVITY.
Insulators are substances which have very high resistivity of the order
of 108 – 1014 Ω m. They offer very high resistance to the flow of current
and are termed non−conductors. Example : glass, mica, amber, quartz,
wood, teflon, bakelite.
13.DEFINE SEMICONDUCTORS BASED ON RESISTIVITY.
In between these two classes of materials lie the semiconductors .They are partially conducting. The resistivity of semiconductor is 10−2 – 104 Ω m. Example : germanium, silicon.
14.What are superconductors,superconductivity?
Ordinary conductors of electricity become better conductors at
lower temperatures. The ability of certain metals, their compounds and
alloys to conduct electricity with zero resistance at very low
temperatures is called superconductivity. The materials which exhibit
this property are called superconductors.
15.Define transition temperature (or) critical temperature.
The temperature at which electrical resistivity of the material suddenly drops to zero and the material changes from normal conductor to a superconductor is called the transition temperature or critical temperature TC.
16.What are the changes observed at transition temperature?
At the transition temperature the following changes are observed :
(i) The electrical resistivity drops to zero.
(ii) The conductivity becomes infinity
(iii) The magnetic flux lines are excluded from the material.
17.STATE FOUR APPLICATIONS OF SUPERCONDUCTORS
(i) Superconductors form the basis of energy saving power systems, namely the superconducting generators,
(ii) Superconducting magnets have been used to levitate trains above its rails. They can be driven at high speed with minimal expenditure of energy.
(iii) the current in a superconducting wire can flow
without any change in magnitude, it can be used for transmission
lines. (iv) Superconductors can be used as memory or storage
elements in computers.
18.WHAT ARE CARBON RESISTORS ?
Carbon resistor consists of a ceramic core,on which a thin layer of crystalline carbon is deposited. These resistors are cheaper, stable and small in size.
19.WHAT ARE COLOUR CODES IN CARBON RESISTORS?
The resistance of a carbon resistor is indicated by the
colour code drawn on it. Black 0, Brown 1, Red 2,Orange 3,Yellow 4
Green 5, Blue 6,Violet 7,Grey 8,White 9.

20.WHAT IS TOLERANCE?GIVE THE VALUES.
The silver or gold ring at one end corresponds to the tolerance. It is
a tolerable range ( + ) of the resistance. The tolerance of silver,
gold, red and brown rings is 10%, 5%, 2% and 1% respectively. If
there is no coloured ring at this end, the tolerance is 20%.

21.WHAT IS THE EFFECTIVE RESISTANCE OF RESISTORS IN SERIES?
RS = R1 + R2 + R3
Thus, the equivalent resistance of a number of resistors in series
connection is equal to the sum of the resistance of individual resistors.
22.WHAT IS THE EFFECTIVE RESISTANCE OF RESISTORS IN PARALLEL?
When a number of resistors are connected in parallel, the sum of the reciprocal of the resistance of the individual resistors is equal to the reciprocal of the effective resistance of the combination
1/RP = 1/R1+1/R2+1/R3.
23.DEFINE THE TEMPERATURE DEPENDENCE OF RESISTANCE.
The temperature coefficient of resistance is defined as the ratio of
increase in resistance per degree rise in temperature to its resistance at
0o C. Its unit is per oC. Rt = Ro (1 + αt)
24.DEFINE INTERNAL RESISTANCE OF A CELL
The electric current in an external circuit flows from the positive
terminal to the negative terminal of the cell, through different circuit
elements. In order to maintain continuity, the current has to flow
through the electrolyte of the cell, from its negative terminal to positive
terminal. During this process of flow of current inside the cell, a
resistance is offered to current flow by the electrolyte of the cell. This
is termed as the internal resistance of the cell.
25. STATE KIRCHOFF’S FIRST LAW (CURRENT LAW)
Kirchoff’s current law states that the algebraic sum of the currents meeting at any junction in a circuit is zero. The current flowing towards a junction is positive and the current flowing away from the junction
is negative. The sum of the currents entering the junction is equal to the sum of the currents leaving the junction. This law is a consequence of
conservation of charges.
26.STATE KIRCHOFF’S SECOND LAW (VOLTAGE LAW)
Kirchoff’s voltage law states that the algebraic sum of the
products of resistance and current in each part of any closed circuit is
equal to the algebraic sum of the emf’s in that closed circuit. This law
is a consequence of conservation of energy.
27.DEFINE “ELECTRIC ENERGY” AND “ELECTRIC POWER”.
Electric power is defined as the rate of doing electric work.
Power = Work done/ time =VIt/t = VI
Electric power is the product of potential difference and current
strength. Since V = IR, Power = I2R
Electric energy is defined as the capacity to do work. Its unit is
joule. In practice, the electrical energy is measured by watt hour (Wh)
or kilowatt hour (kWh). 1 kWh is known as one unit of electric energy.
1 kWh = 1000 Wh = 1000 × 3600 J = 36 × 105 J

28.WHAT IS WATTMETER?
A wattmeter is an instrument used to measure electrical power
consumed i.e energy absorbed in unit time by a circuit. The wattmeter
consists of a movable coil arranged between a pair of fixed coils in the
form of a solenoid. A pointer is attached to the movable coil. The free
end of the pointer moves over a circular scale. When current flows
through the coils, the deflection of the pointer is directly proportional
to the power.
29.STATE FARADAY’S FIRST LAW OF ELECTROLYSIS
The mass of a substance liberated at an electrode is directly proportional to the charge passing through the electrolyte.
If an electric current I is passed through an electrolyte for a time
t, the amount of charge (q) passed is I t. According to the law, mass of
substance liberated (m) is m α q or m = zIt
where Z is a constant for the substance being liberated called as
electrochemical equivalent. Its unit is kg C–1.
30.DEFINE ELECTROCHEMICAL EQUIVALENT.
The electrochemical equivalent of a substance is defined as the
mass of substance liberated in electrolysis when one coulomb charge
is passed through the electrolyte. m = zIt
where Z is a constant for the substance being liberated called as
electrochemical equivalent. Its unit is kg C–1.
31.STATE STATE FARADAY’S SECOND LAW OF ELECTROLYSIS
The mass of a substance liberated at an electrode
by a given amount of charge is proportional to the *chemical equivalent
of the substance. If E is the chemical equivalent of a substance, from the second law m α E
32.STATE THE APPLICATIONS OF SECONDARY CELLS.
The secondary cells are rechargeable. They have very low internal
resistance. Hence they can deliver a high current if required. They can
be recharged a very large number of times without any deterioration in
properties. These cells are huge in size. They are used in all
automobiles like cars, two wheelers, trucks etc. The state of charging
these cells is, simply monitoring the specific gravity of the electrolyte.
It should lie between 1.28 to 1.12 during charging and discharging
respectively.

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