Physics-DPP-2-Electromagnetic Induction & Alternating current

PHYSICS Topic: E. M. I and A/C Date: 1. Two coils X and Y are placed in a circuit such that the current changes by amp in coil X and the magnetic flux changes by 0.4 weber in Y. The value of mutual inductance of the coils and its unit is: (a) 0.2 henry (b) 5 henry (c) 0.8 henry (d) 0.2 weber 2. A coil of wire of a certain radius has 600 turns and a self-inductance of 108 mH. The self-inductance of a second similar coil of 500 turns will be: (a) 74 mH (b) 75 mH (c) 76 mH (d) 77 mH 3. An electric bulb in series with a large inductor when connected across a DC source takes a little time before reaching a stable glow. If an iron core is inserted into the inductor, the delay will: (a) increase (b) decrease (c) remain the same (d) may change in either direction depending upon the values of inductance and resistance 4. Two coils of self-inductances L1 and L2 are placed so close to each other that the effective flux in one coil is completely linked with the other; then the mutual inductance M between them is given by: (a) M = (b) M = L1 – L2 (c) M = L1 / L2 (d) M = L1 + L2 5. A solenoid of length 1 metre has self-inductance L henry. If number of turns are doubled, its self-inductance: (a) remains same (b) becomes 3L henry (c) becomes 4L henry (d) becomes L / henry 6. The mutual inductance of an induction coil is 5 H. In the primary coil, the current reduces from 5 Ato zero in 10–3 sec. What is the induced e.m.f. in the secondary coil? (a) 2500 V (b) 25000V (c) 2510 V (d) Zero 7. A wire cd of length l and mass m is sliding without friction on conducting rails ax and by as shown. The vertical rails are connected to each other with a resistance R between a and b. Auniform magnetic field B is applied perpendicular to the plane abcd such the cd moves with a constant velocity of: (a) mgR Bl (b) mgR B2l 2 (c) mgR B3l 3 (d) mgR B2l PHYSICS Topic: E. M. I and A/C Date: 8. A wheel having metal spokes of 1 m long between its axle nad rim is rotating in a magnetic field of flux density 22 5 × 10–5 T normal to the plane of the wheel. An e.m.f. of 7 mV is produced between the rim and the axle of the wheel. The rate of rotation of the wheel in radians per second is: (a) 10 (b) 20 (c) 30 (d) 40 9. The average e.m.f. induced in a coil when a current changes from 0 to 2 A in 0.05 sec is 8V. The self-inductance of the coil is: (a) 0.1 H (b) 0.2 H (c) 0.4 H (d) 0.8 H 10. In an inductor of self-inductance L = 2 mH, current changes with time according to relation I = t2 e–t. At what time e.m.f. is zero? (a) 4 s (b) 3 s (c) 2 s (d) 1 s *****End of Paper***** PHYSICS Topic: E. M. I and A/C Answer key Date: 1.(a) 2.(b) 3. (a) 4. (a) 5. (c) 6. (b) 7. (b) 8. (b) 9. (b) 10. (c)

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