#### Electromagnetic Induction and Alternating Current One Mark Questions with Answer

12th Standard EM

Reg.No. :
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Physics

Time : 00:45:00 Hrs
Total Marks : 25
25 x 1 = 25
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)

2. Electromagnetic induction is-not used in

(a)

transformer

(b)

room heater

(c)

AC generator

(d)

choke coil

3. 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

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

(a)

input current

(b)

input voltage

(c)

input power

(d)

all

5. 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

6. In the following figure the key is dosed. Which statement is correct?

(a)

momentary current flowsin Y circuit from Bto A

(b)

momentary current flowsin Y circuit from A to B

(c)

no current flows along AB

(d)

the coil Y is attracted to X

7. Which current- time graph represents the steady movement of short magnet through a coil XY?

(a)

(b)

(c)

(d)

8. The unit of self inductance is

(a)

Henry

(b)

Ampere

(c)

(d)

Ohm

9. The self inductance of a coil is

(a)

directly proportional to N

(b)

inversely proportional to N

(c)

directly proportional to N2

(d)

inversely proportional to N2

10. The self-inductance Lof a solenoid is given as

(a)

$L=\frac { { \mu }_{ o }NA }{ l }$

(b)

$L=\frac { { \mu }_{ o }{ NA }^{ 2 } }{ l }$

(c)

$L=\frac { { \mu }_{ o }{ N }^{ 2 }A }{ l }$

(d)

$L=\frac { { { \mu }_{ o }A } }{ Nl }$

11. The generator rule is

(a)

Fleming's left hand rule

(b)

Fleming's right hand rule

(c)

Maxwell's right hand cork screw rule

(d)

Right hand palm rule

12. Eddy currents was first observed by

(a)

Foucault

(b)

Newton

(c)

(d)

Fleming

13. 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

14. The necessary magnetic field for a low power a.c generator is produced by _________

(a)

electric coil

(b)

permanent magnets

(c)

electromagnets

(d)

batteries

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

(a)

silicon

(b)

plastic

(c)

carbon

(d)

nylon

16. __________ principle is used in transformer.

(a)

mutual induction

(b)

electromagnetic induction

(c)

self induction

(d)

eddy currents

17. A transformer

(a)

converts energy

(b)

changes voltage

(c)

changes current

(d)

changes both current and voltage

18. The efficiency of an ideal transformer is

(a)

0

(b)

1

(c)

infinite

(d)

none

19. In an a.c. circuit with an inductor

(a)

voltage lags current by π/2

(b)

voltage and current are in phase

(c)

(d)

current lags voltage by π/2

20. Inductive reactance, XL = ?

(a)

2πnL

(b)

$\frac { 2\pi v }{ L }$

(c)

$\frac { 2\pi }{ vL }$

(d)

$\frac { 2\pi }{ vL }$

21. Unit of inductive reactance is ___________

(a)

ohm-metre

(b)

mho-metre-1

(c)

ohm

(d)

mho

22. The unit of impedance is ________________

(a)

mho-metre-1

(b)

ohm

(c)

ohm-metre

(d)

mho-metre

23. For normal frequencies, the range of Q- factor is from,

(a)

1 to 10

(b)

10 to 100

(c)

100 to 1000

(d)

101 to 999

24. The Q factor of an a.c. circuit containing a resistance R, inductance L and capacitor C is

(a)

$Q=\frac { 1 }{ \sqrt { LC } }$

(b)

$Q=\frac { 1 }{ R } \sqrt { \frac { C }{ L } }$

(c)

$Q=\frac { 1 }{ R } \sqrt { \frac { L }{ C } }$

(d)

$Q=\frac { 1 }{ \sqrt { LR } }$

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

(a)

$\phi$sin$\phi$

(b)

cosec $\phi$

(c)

cos $\phi$

(d)

tan $\phi$