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#### 12th Standard Physics Electromagnetic Induction and Alternating Current English Medium Free Online Test One Mark questions with Answer Key 2020 - 2021

12th Standard EM

Reg.No. :
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Physics

Time : 00:20:00 Hrs
Total Marks : 20

20 x 1 = 20
1. When the current changes from +2A to −2A in 0.05 s, an emf of 8 V is induced in a coil. Th e co-efficient of self-induction of the coil is

(a)

0.2H

(b)

0.4H

(c)

0.8H

(d)

0.1H

2. 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 μH

(b)

8.54 μH

(c)

9.54 μH

(d)

10.54 μH

3. In a series RL circuit, the resistance and inductive reactance are the same. Then the phase difference between the voltage and current in the circuit is

(a)

$\frac{\pi}{4}$

(b)

$\frac{\pi}{2}$

(c)

$\frac{\pi}{6}$

(d)

zero

4. An inductor 20 mH, a capacitor 50 μF and a resistor 40 Ω 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

5. Lenz's law is in accordance with the law of

(a)

conservation of charges

(b)

conservation of flux

(c)

conservation of momentum

(d)

conservation of energy

6. The self-inductance of a straight conductor is

(a)

zero

(b)

infinity

(c)

very large

(d)

very small

7. An emf of 12V is induced when the current in the coil changes at the rate of 40 A S-1. The coefficient of self induction of the coil is

(a)

0.3 H

(b)

0.003 H

(c)

30 H

(d)

4.8 H

8. Which of the following cannot be stepped up in a transformer?

(a)

input current

(b)

input voltage

(c)

input power

(d)

all

9. If a secondary coil has 40 turns, and a primary coil with 20 turns is charged with 50V of potential difference, then potential difference in secondary would be

(a)

50 V

(b)

25 V

(c)

60 V

(d)

100 V

10. The unit of self inductance is

(a)

Henry

(b)

Ampere

(c)

(d)

Ohm

11. A phenomenon in which a varying current in one coil induces an emf in the neighbouring coil is

(a)

mutual induction

(b)

self induction

(c)

electrostatic induction

(d)

electromagnetic induction

12. The property of a coil which enables to produce an opposite induced emf in it when the current in the coil changes is called _______________

(a)

electromagnetism

(b)

self - induction

(c)

mutual induction

(d)

parallel- induction

13. In an a.c generator, the brushes are made of __________

(a)

silicon

(b)

plastic

(c)

carbon

(d)

nylon

14. In an a. c. dynamo, the induced current is _________ in nature.

(a)

alternating

(b)

increasing

(c)

decreasing

(d)

constant

15. __________ principle is used in transformer.

(a)

mutual induction

(b)

electromagnetic induction

(c)

self induction

(d)

eddy currents

16. The efficiency of an ideal transformer is

(a)

0

(b)

1

(c)

infinite

(d)

none

17. The voltage drop across the resistor in a LCR series circuit is __________________

(a)

VR = IR

(b)

VR = IR2

(c)

VR = I/R

(d)

VR=R/I

18. Unit of inductive reactance is ___________

(a)

ohm-metre

(b)

mho-metre-1

(c)

ohm

(d)

mho

19. The power factor of an a.c, circuit is _________

(a)

$\phi$sin$\phi$

(b)

cosec $\phi$

(c)

cos $\phi$

(d)

tan $\phi$

20. The instantaneous current in an AC circuit containing a pure inductor is i = Io sinωt, The instantaneous emf is: The

(a)

e = Eosin$\left( \omega t+\frac { \pi }{ 2 } \right)$

(b)

e = Eosin$\left( \omega t-\frac { \pi }{ 2 } \right)$

(c)

e=Eosin(ωt - π)

(d)

e = Eosin