#### Most important one mark questions physics chapter one

12th Standard EM

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Physics

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

Part - A

20 x 1 = 20
1. If C is the capacitance of an air filled capacitor and C is the capacitance of dielectric filled capacitor, then

(a)

C'εrC'

(b)

$C'=\frac { C }{ { \varepsilon }_{ r } }$

(c)

$C'=\frac { { \varepsilon }_{ r } }{ C }$

(d)

$C'={ \varepsilon }_{ 0 }{ \varepsilon }_{ r }$

2. The capacitance of a parallel plate capacitor increases from 5μf of 50μf when a dielectric is filled between the plates. The permitivity of the dielectric is

(a)

8.854x10-12C2N-1 m-2

(b)

8.854x10-11C2N-1 m-2

(c)

10x10-12C2N-1 m-2

(d)

12x10-12C2N-1 m-2

3. An electric dipole placed at an angle in a nonuniform electric field experiences

(a)

neither a force nor a torque

(b)

torque

(c)

both force and torque

(d)

force only

4. Two copper spheres A and B of same size are charged to same potential. A is hollow and B is solid. Which of the two holds more charge?

(a)

Solid sphere cannot hold any charge

(b)

hollow sphere cannot hold any charge

(c)

both have zero charge

(d)

both have the same charge

5. A bird sitting an a high power line

(a)

gets killed instantly

(b)

gets a mild shock

(c)

is not affected practically

(d)

gets a fatal shock

6. Two conducting charged spheres x and y having unequal charges are connected by a wire. Which of the following is true?

(a)

charge is conserved

(b)

electrostatic energy is conserved

(c)

both the charge and electrostatic energy are conserved

(d)

neither of these is conserved

7. Which of the following statement on equipotential surface is wrong?

(a)

The potential difference between any two points on the surface, is zero.

(b)

The electric field is always perpendicular to the surface

(c)

Equipotential surface is always spherical.

(d)

No work is done in moving a charge along the surface

8. Two identical metal balls with charges +2Q and -Q are separated by some distance and exerts a force F on each other. They are joined by a conducting wire, which is then removed. The force between them will now.

(a)

F/8

(b)

F/12

(c)

F

(d)

F/4

9. A spherical equipotential surface is not possible

(a)

for a point charge

(b)

for a dipole

(c)

inside a spherical capacitor

(d)

inside a uniformly charged sphere

10. Charge Q is divided into two parts which are then kept some distance apart. The force between them will be maximum if the two parts are

(a)

$\frac{Q}{2}$ each

(b)

each $\frac{Q}{5}$

(c)

$\frac{Q}{3}$and$\frac{2Q}{3}$

(d)

$\frac{Q}{4}$and$\frac{3Q}{4}$

11. In a parallel plate capacitor of capacitance C, a metal sheet is inserted between the plates, parallel to them. The thickness of the sheet is half of the separation between the plates. The capacitance now becomes

(a)

2C

(b)

$\frac{C}{4}$

(c)

4C

(d)

$\frac{C}{2}$

12. When 4V emf is applied across a 1F capacitor, it will store energy of

(a)

2J

(b)

4J

(c)

6J

(d)

8J

13. Value of k in Coulomb's law depends upon

(a)

magnitude of charges

(b)

distance between charges

(c)

both (a) and (b)

(d)

medium between two charges

14. Region around a charge q in which it exerts force on a test charge is called

(a)

electric flux intensity

(b)

electric force

(c)

electric field

(d)

Coulomb's force

15. Which of the following cannot be the units of electric field intensity?

(a)

NC-1

(b)

Vm-1

(c)

JC-1/m

(d)

JC-1

16. The electric flux through a surface will be minimum when the angle between Eand A is

(a)

90°

(b)

60°

(c)

(d)

45°

17. One Joule per Coulomb is called

(a)

Gauss

(b)

ampere

(c)

(d)

volt

18. When three capacitors are joined in series, the total capacitance is

(a)

Equal to the sum of the capacitance

(b)

Greater than the value of the maximum capacitance

(c)

Less than the value of the mininim capacitance

(d)

none of the above

19. The concentric spheres of radii R and r have similar charges with equal surface densities (σ). What is the electric potential at their common centre?

(a)

$\frac { \sigma }{ { \varepsilon }_{ 0 } } (R-r)$

(b)

$\frac { \sigma }{ { { \varepsilon }_{ 0 } } } (R+r)$

(c)

$R\frac { \sigma }{ { \varepsilon }_{ 0 } }$

(d)

$\frac { \sigma }{ { \varepsilon }_{ 0 } }$

20. A charge QμC is placed at the center of a cube. The flux coming out from any surface will be

(a)

$\frac { Q }{ { 24\varepsilon }_{ 0 } }$

(b)

$\\ \frac { Q }{ { 8\varepsilon }_{ 0 } }$

(c)

$\frac { Q }{ { 6\varepsilon }_{ 0 } } \times { 10 }^{ -6 }$

(d)

$\frac { Q }{ { 6\varepsilon }_{ 0 } } \times { 10 }^{ -3 }$