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#### 12th Standard Physics Electromagnetic Induction and Alternating Current English Medium Free Online Test One Mark questions 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. 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. Th e fl ux linked with a coil at any instant t is given by $\Phi$B =10t2−50t+ 250 . The induced emf at t = 3s is

(a)

−190 V

(b)

−10 V

(c)

10 V

(d)

190 V

3. 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

4. The instantaneous values of alternating current and voltage in a circuit are $i=\frac { 1 }{ \sqrt { 2 } } sin\left( 100\pi t \right)$ A and v=$=\frac { 1 }{ \sqrt { 2 } } sin\left( 100\pi t+\frac { \pi }{ 3 } \right) V.$The average power in watts consumed in the circuit is

(a)

$\frac{1}{4}$

(b)

$\frac{\sqrt3}{4}$

(c)

$\frac{1}{2}$

(d)

$\frac{1}{8}$

5. Electromagnetic induction is-not used in

(a)

transformer

(b)

room heater

(c)

AC generator

(d)

choke coil

6. The unit henry can also be written as

(a)

VS A-1

(b)

Wb A-1

(c)

Ωs

(d)

all

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. Transformer works on

(a)

AC only

(b)

DC only

(c)

both AC and DC

(d)

AC more effectively than DC

9. The magnitude of the induced emf in a conductor depends on the

(a)

flux density of the magnetic field

(b)

amount of flux cut

(c)

(d)

rate of change of flux

10. 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

11. In Fleming's right hand rule, the forefinger represents the direction of

(a)

motion of the conductor

(b)

magnetic field

(c)

induced current

(d)

induced emf

12. 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

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

(a)

electric coil

(b)

permanent magnets

(c)

electromagnets

(d)

batteries

14. A transformer

(a)

converts energy

(b)

changes voltage

(c)

changes current

(d)

changes both current and voltage

15. Flux loss can be minimized using ________ core.

(a)

laminated

(b)

shell-type

(c)

perforated

(d)

sheet-type

16. An alternating current has

(a)

only positive value

(b)

only negative value

(c)

both positive and negative value

(d)

17. Inductive reactance, XL = ?

(a)

2πnL

(b)

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

(c)

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

(d)

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

18. In LCR series circuit, at resonance is ___________

(a)

impedance (Z) is maximum

(b)

current is minimum

(c)

impedance (Z) is equal to R

(d)

vo = $\frac{1}{LC}$

19. The average power consumed per cycle is:

(a)

Zero

(b)

2000 W

(c)

1000 W

(d)

500 W

20. In RLC series AC circuit at resonance:

(a)

Resistance is zero

(b)

Net reactance is zero

(c)

impedance is maximum

(d)

voltage leads the current by a phase angle $\frac{ㅠ}{2}$