#### Important one mark questions

12th Standard EM

Reg.No. :
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Physics

Use blue pen only
Time : 00:10:00 Hrs
Total Marks : 20

Part A

20 x 1 = 20
1. Two identical point charges of magnitude –q are fi xed as shown in the fi gure below. A third charge +q is placed midway between the two charges at the point P. Suppose this charge +q is displaced a small distance from the point P in the directions indicated by the arrows, in which direction(s) will +q be stable with respect to the displacement

(a)

A1 and A2

(b)

B1 and B2

(c)

both directions

(d)

No stable

2. Which charge configuration produces a uniform electric field?

(a)

point Charge

(b)

infinite uniform line charge

(c)

uniformly charged infinite plane

(d)

uniformly charged spherical shell

3. An electric dipole is placed at an alignment angle of 300 with an electric fi eld of 2 × 105 NC-1. It experiences a torque equal to 8 N m. Th e charge on the dipole if the dipole length is 1 cm is

(a)

4 mC

(b)

8 mC

(c)

5 mC

(d)

7 mC

4. Four Gaussian surfaces are given below with charges inside each Gaussian surface. Rank the electric fl ux through each Gaussian surface in increasing order.

(a)

D < C < B < A

(b)

A < B = C < D

(c)

C < A = B < D

(d)

D > C > B > A

5. Two identical conducting balls having positive charges q1 and q2 are separated by a center to center distance r. If they are made to touch each other and then separated to the same distance, the force between them will be

(a)

less than before

(b)

same as before

(c)

more than before

(d)

zero

6. Rank the electrostatic potential energies for the given system of charges in increasing order.

(a)

1 = 4 < 2 < 3

(b)

2 = 4 < 3 < 1

(c)

2 = 3 < 1 < 4

(d)

3 < 1 < 2 < 4

7. An electric field $\vec { E } =10x\hat { i }$ exists in a certain region of space. Then the potential difference V = Vo – VA, where Vo is the potential at the origin and VA is the potential at x = 2 m is:

(a)

10 J

(b)

-20 J

(c)

+20 J

(d)

-10 J

8. A thin conducting spherical shell of radius R has a charge Q which is uniformly distributed on its surface. The correct plot for electrostatic potential due to this spherical shell is

(a)

(b)

(c)

(d)

9. Two points A and B are maintained at a potential of 7 V and -4 V respectively. The work done in moving 50 electrons from A to B is

(a)

8.80 × 10-17 J

(b)

-8.80 × 10-17 J

(c)

4.40 × 10-17 J

(d)

5.80 × 10-17 J

10. If voltage applied on a capacitor is increased from V to 2V, choose the correct conclusion

(a)

Q remains the same, C is doubled

(b)

Q is doubled, C doubled

(c)

C remains same, Q doubled

(d)

Both Q and C remain same

11. A parallel plate capacitor stores a charge Q at a voltage V. Suppose the area of the parallel plate capacitor and the distance between the plates are each doubled then which is the quantity that will change?

(a)

Capacitance

(b)

Charge

(c)

Voltage

(d)

Energy density

12. Three capacitors are connected in triangle as shown in the figure. The equivalent capacitance between the points A and C is

(a)

1μF

(b)

2μF

(c)

3μF

(d)

$\frac{1}{4}$μF

13. Two metallic spheres of radii 1 cm and 3 cm are given charges of -1 x 10-2 C and 5 x 10-2 C respectively. If these are connected by a conducting wire, the final charge on the bigger sphere is

(a)

3 × 10-2 C

(b)

4 × 10-2 C

(c)

1 × 10-2 C

(d)

2 × 10-2 C

14. Based on Franklin's convention amber rods are_________.

(a)

positively charged

(b)

negatively charged

(c)

neutral

(d)

none of the above

15. The electrostatic force obeys _______.

(a)

Newton's I law

(b)

Newton's II law

(c)

Newton's III law

(d)

none of the above

16. In electrostatics if the charges are in motion, another force named __________ comes into play in addition to coulomb force

(a)

Lorentz force

(b)

Repulsive force

(c)

Attractive force

(d)

electromagnetic force

17. The value of constant 'K' in coulomb law is

(a)

0.9 x 109 Nm2 C2

(b)

9 x 10-9 Nm2C2

(c)

9 x 109 Nm-2 C-2

(d)

9 x 109 Nm2 C-2

18. The electrostatic force is always greater in magnitude than gravitational force for_________ object.

(a)

bigger size

(b)

smaller size

(c)

medium size

(d)

all the above

19. The relative permittivity of water is _______.

(a)

εr= 70

(b)

εr=75

(c)

εr=80

(d)

εr=85

20. _______ and Coulomb's law form fundamental principles of electrostatics

(a)

Newton's law of gravitation

(b)

superposition principle

(c)

ohm's law

(d)

Kepler's law