## Thursday, November 25, 2010

### SRIRAM

 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?