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DEPARTMENT OF PHYSICS, , Physics, Time : 1.00 hr xi Marks : 20, , E.m. Induction And A.c. Current |, , 1) When a circular coil of radius 1 m and 100 turns is rotated in a horizontal uniform magnetic, field, the peak value of e.m.f. induced is 100 V. The coil is unwound and then rewound into a, circular coil of radius 2m. If it is rotated, now with the same speed, under similar conditions,, the new peak value of e.m.f. developed is :, , A) 50V B) 25V Cc) 100 V D) 200 V., , 2) Acircular coil of mean radius of 7 cm and having 4000 turns is rotated at the rate of 1800, revolutions per minute In the earths magnetic field (B = 0.5 gauss), the maximum e.m.f., induced in coil will be:, , A) 1.158 V B) 0.58 V C) 0.29V D)5.8V, , 3) A0O.1 m long conductor carrying a current of 50 A is held perpendicular to a magnetic field of, 1.25 mT. The mechanical power required to move the conductor with a speed of ms"! is:, , A) 62.5 mw B) 625 mw C) 6.25 mw D) 12.5 mw, , 4) A solenoid has 2000 turns wound over a length of 0.30 metre. The area of its cross-section in, 1.2 x 10m? . Around its central section, a coil of 300 turns is wound. If an initial current of, 2A in the solenoid is reversed in 0.25 s, then the e.m.f. induced in the coil is :, , A)6x10V B)8x10-?V C)6 mv D) 48 mv, , 5) Two circults have coefficient of mutual induction of 0.09 H. Average e.m.f. induced In the, secondary by a change of current from 0 to 20 A in 0.006 second in the primary will be :, , A) 120V B) 80V C) 200 V D) 300 V, , 6) When the number of turns and the length of the solenoid are doubled keeping the area of, cross-section same, the inductance, , A) Remains the same _B) Is halved C) Is doubled D) Becomes four, times, , 7) When the current through a solenoid increases at a constant rate, the induced current, A) Is constant and is in the direction of the inducing current., B) Is constant and is opposite to the direction of the inducing current., C) Increases with time and is in the direction of the inducing current., , D) Increases with time and opposite to the direction of the inducing current.
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8) A solenoid is placed inside another solenoid, the length of both being equal carrying same, magnitude of current. The parameters like radius and number of turns are in the ratio 1 : 2 for, the two solenoids. The mutual inductance on each other would be :, , A) Miz = Mar B) Mi2 = 2Ma1 C) 2Mi2 = Mar D) Miz = 4May, , 9) If acurrent of 5 Ain a coil of self inductance 2 mH is cut off in time 0.1 s, the induced emf in, the coil is :, , A)O1V B) 0.01 V c)o.2Vv D) 0.02 V, , 10) A transformer of efficiency 90% draws an input power of 4 kW. An electrical appliance, connected across the secondary draws a current of 6A. The impedance of the device Is :, , A) 600 B) 500 c)s800 D) 100 0, 11) The induction coil works on the principle of, , A) Self-induction B) Mutual induction, , C) Ampere”s rule D) Fleming"s right hand rule, , 12) A transformer with efficiency 80% works at 4 kW and 100 V. If the secondary voltage is 200 V,, then the primary and secondary currents are respectively., , A) 40 A, 164 B) 16A,40A C) 20A, 40A D) 40A, 20A., , 13) A step-down transformer is connected to main supply 200 V to operate a 6V, 30W bulb. The, current in primary is :, , A)3A B)15Aa C)O3A D)O15A, , 14) A step-down transformer is used an a 1000 V line to deliver 20 A at 120 V at the secondary, coil. If the efficiency of the transformer is 80% the current drawn from the line is :, , A)3A B)30A Cosa D244, 15) In an A.C. generator, when the plane of the armature is perpendicular to the magnetic field, , A) Both magnetic flux and emf are maximum, B) Both magnetic flux and emf are zero, C) Both magnetic flux and emf are half of their respective maximum values, , D) Magnetic flux is maximum and emf is zero, , 16) In an ideal transformer the number of turns of primary and secondary coil is given as 100 and, 300 respectively. If the power input is 60 W, the power output is :
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A) 100 W B) 300 W c) 180 W D) 60W, , 17) Two circular coils can be arranged in any of the three situations shown in Fig. Their mutual, inductance will be :, , o)~ «(Ct, a> cD <>), , A) maximum in situation (A) B) maximum in situation (B), , C) maximum in situation (C) D) the same in all situations., , 18) A metallic square loop ABCD is moving in its own plane with velocity v in a uniform magnetic, field perpendicular to its plane as shown in Fig. An electric field is induced :, , see, , ., ., , , , A) In AD, but not in BC B) in BC, but not in AD, , C) neither in AD nor in BC D) in both AD and BC, , 19) In an inductor, the current | (in ampere) varies with time t (in second) as | = 5+16t If the emf, induced in the inductor is 10 mV, what is its self inductance ?, , A) 6.25 x 10™4H B) 6.25 x 10°9H C)7.5 x 10H D) 7.5 « 10°H, 20) In Q. 22 above, the power supplied to the inductor at t= 1 sis:, , A) 0.021 W B)0.21W c)21W D)21W