Electromagnetic Induction And Alternating Current Book Back Questions & Answers
Unit 4 > Physics > Class 12 > Samacheer Kalvi - English Medium
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1. An electron moves on a straight line path XY as shown in the figure. The coil abcd is adjacent to the path of the electron. What will be the direction of current, if any, induced in the coil?
(a) The current will reverse its direction as the electron goes past the coil
(b) No current will be induced
(c) abcd
(d) adcb
Correct answer: (a) The current will reverse its direction as the electron goes past the coil
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2. A thin semi-circular conducting ring (PQR) of radius r is falling with its plane vertical in a horizontal magnetic field B, as shown in the figure. P R r Q The potential difference developed across the ring when its speed v , is
(a) Zero
(b) B r v 2/ 2 and P is at higher potential
(c) rBv and R is at higher potential
(d) 2rBv and R is at higher potential
Correct answer: (d) 2rBv and R is at higher potential
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3. The flux linked with a coil at any instant t is given by B = 10t t 50 + 250 2 . The induced emf at t = 3 s is
(a) 190 V
(b) 10 V
(c) 10 V
(d) 190 V
Correct answer: (b) 10 V
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4. When the current changes from +2A to 2A in 0.05 s, an emf of 8 V is induced in a coil. The co-efficient of self-induction of the coil is
(a) 0.2 H
(b) 0.4 H
(c) 0.8 H
(d) 0.1 H
Correct answer: (d) 0.1 H
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5. A circular coil with a cross-sectional area of 4 cm2 has 10 turns. It is placed at the centre of a long solenoid that has 15 turns/cm and a cross-sectional area of 10 cm2 . The axis of the coil coincides with the axis of the solenoid. What is their mutual inductance?
(a) 7.54 H
(b) 8.54 H
(c) 9.54 H
(d) 10.54 H
Correct answer: (a) 7.54 H
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6. In a transformer, the number of turns in the primary and the secondary are 410 and 1230 respectively. If the current in primary is 6A, then that in the secondary coil is
(a) 2 A
(b) 18 A
(c) 12 A
(d) 1 A
Correct answer: (a) 2 A
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7. A step-down transformer reduces the supply voltage from 220 V to 11 V and increase the current from 6 A to 100 A. Then its efficiency is
(a) 1.2
(b) 0.83
(c) 0.12
(d) 0.9
Correct answer: (b) 0.83
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8. In an electrical circuit, R, L, C and AC voltage source are all connected in series. When L is removed from the circuit, the phase difference between the voltage and current in the circuit is 3 . Instead, if C is removed from the circuit, the phase difference is again 3 . The power factor of the circuit is (NEET 2012)
(a) 1 2
(b) 1 2
(c) 1
(d) 3 2
Correct answer: (c) 1
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9. In a series RL circuit, the resistance and inductive reactance are the sameThen the phase difference between the voltage and current in the circuit is.
(a) / 4
(b) / 2
(c) /6
(d) zero
Correct answer: (a) / 4
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10. In a series resonant RLC circuit, the voltage across 100 resistor is 40 V. The resonant frequency is 250 rad/s. If the value of C is 4 F, then the voltage across L is
(a) 600 V
(b) 4000 V
(c) 400V
(d) 1 V
Correct answer: (c) 400V
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11. An inductor 20 mH, a capacitor 50 F and a resistor 40 are connected in series across a source of emf V = 10 sin 340 t. The power loss in AC circuit is
(a) 0.76 W
(b) 0.89 W
(c) 0.46 W
(d) 0.67 W
Correct answer: (c) 0.46 W
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12. The instantaneous values of alternating current and voltage in a circuit are i t = ( ) 1 2 sin 100 A and v = + 1 2 100 3 sin t V. The average power in watts consumed in the circuit is
(a) 1/ 4
(b) 3/ 4
(c) 1/ 2
(d) 1 /8
Correct answer: (d) 1 /8
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13. In an oscillating LC circuit, the maximum charge on the capacitor is Q. The charge on the capacitor when the energy is stored equally between the electric and magnetic fields is
(a) Q/ 2
(b) Q/ 3
(c) Q/ 2
(d) Q
Correct answer: (c) Q/ 2
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14. 20 2 H inductor is connected to a capacitor of capacitance C. The value of C in order to impart maximum power at 50 Hz is
(a) 50 F
(b) 0.5 F
(c) 500 F
(d) 5 F
Correct answer: (d) 5 F