#### Chepter one centum multiple choice questions

12th Standard EM

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Physics

Dont write anything on the question paper
Time : 00:15:00 Hrs
Total Marks : 20

Part - A

20 x 1 = 20
1. The expression for the electric field due to a surface of total charge 'Q' is given by

(a)

$\overset { \rightarrow }{ E } =\frac { 1 }{ 4\pi { \varepsilon }_{ 0 } } \int { \frac { \sigma dA }{ { r }^{ 2 } } } \hat { r }$

(b)

$\overset { \rightarrow }{ E } =\frac { 1 }{ 4\pi { \varepsilon }_{ 0 } } \int { \frac { \rho dA }{ { r }^{ 2 } } } \hat { r }$

(c)

$\overset { \rightarrow }{ E } =\frac { 1 }{ 4\pi { \varepsilon }_{ 0 } } \int { \frac { \lambda dl }{ { r }^{ 2 } } } \hat { r }$

(d)

$\overset { \rightarrow }{ E } =\frac { 1 }{ 4\pi { \varepsilon }_{ 0 } } \int { \frac { dq }{ { r }^{ 2 } } } \hat { r }$

2. The dipole is called point dipole when the distance

(a)

2a approaches infinity and q approaches zero

(b)

2a approaches zero and q approaches infinity

(c)

2a approaches zero and q approaches zero

(d)

2a approaches infinity and q approaches infinity

3. The magnitude of torque on dipole is maximum if

(a)

θ=0o

(b)

θ=90o

(c)

θ=180o

(d)

θ=180o

4. The magnitude of electric dipole moment of water molecule is

(a)

6 x 10-30 cm

(b)

6.2 x 10-30 cm

(c)

6.1 x 10-30

(d)

5.95 10-30 cm

5. The expression for electric potentid difference is

(a)

$\int _{ R }^{ P }{ +\overset { \rightarrow }{ E } .\overset { \rightarrow }{ dr } }$

(b)

$\\ -\int _{ \infty }^{ P }{ +\overset { \rightarrow }{ E } .\overset { \rightarrow }{ dr } }$

(c)

$\\\int _{ \infty }^{ P }{ \overset { \rightarrow }{ E } .\overset { \rightarrow }{ dr } }$

(d)

$\int _{ R }^{ P }{ -\overset { \rightarrow }{ E } .\overset { \rightarrow }{ dr } }$

6. At Infinity (i.e r = ∞), the electrostatic potential (V) is

(a)

(b)

maximum

(c)

minimum

(d)

Zero

7. The potential due to a single point charge falls as

(a)

$\frac { 1 }{ { r }^{ 2 } }$

(b)

$\frac { 1 }{ { r }^{ 3 } }$

(c)

$\frac { 1 }{ { r }^{ } }$

(d)

-$\frac { 1 }{ { r }^{ } }$

8. The unit for electric flux is

(a)

C2N-1m-2

(b)

Nm2C-2

(c)

Nm2C-1

(d)

Nm-2C-1

9. The electric flux is negative, if the angle between $\overset { \rightarrow }{ dA }$ and $\overset { \rightarrow }{ E }$ is

(a)

Less than 90°

(b)

greater than 90°

(c)

equal to 90°

(d)

equal to 0°

10. The time taken by a conductor to reach electrostatic equilibrium is in the order of

(a)

10-18

(b)

10-14s

(c)

10-16 s

(d)

10-20 s

11. A non-conducting material which has no free electrons is called

(a)

capacitor

(b)

Dielectric

(c)

conductor

(d)

Inductor

12. The unit for electric susceptibility is

(a)

Nm2 C-2

(b)

C2 N-1 m-2

(c)

C-2Nm2

(d)

N-1 m-2C2

13. In the given cricuit the effective capacitance between A and B will be

(a)

3μf

(b)

$\frac{36}{13}$ μf

(c)

13μf

(d)

7μf

14. The direction of electric field at a point the equatorial line due to an electric dipole is

(a)

along the equatorial line towards the dipole.

(b)

along the equatorial line away from the dipole

(c)

parallel to the axis of the dipole and opposite to the direction of dipole moment

(d)

parallel to the axis of the dipole and in the direction of dipole moment.

15. The lower comb of van de graaff generator is maintained at a positive potential of

(a)

10 kV

(b)

107 V

(c)

100 V

(d)

103 V

16. The negative gradient of potential is

(a)

torque

(b)

electric current

(c)

electric field intensity

(d)

electric force

17. Two charges are kept at a distance in air what should be the relative permittivity of the medium in which the two charges should be kept at the same distance so that they experience half of the force which they experienced in air?

(a)

$\frac{1}{2}$

(b)

$\frac{1}{0.2}$

(c)

2

(d)

0.2

18. An uniformly charged conducting shell of 2cm diameter has a surface charge density of 80μC / m2. The charge on the shell is

(a)

100.48 nC

(b)

100.48 μC

(c)

100.48C

(d)

100.48x10-12C

19. In tuning radio we use,

(a)

capacitors

(b)

transistors

(c)

diodes

(d)

LEDS

20. Dielectric constant for the metals is

(a)

Zero

(b)

>1

(c)

<1

(d)

Infinite