Electrostatics MCQs

Question 1

Two identical capacitors have the same capacitance C. One of them is charged to potential V1 and the other to V2. The negative ends of the capacitors are connected together. When the positive ends are also connected, the decrease in energy of the combined system is:

Accepted Answer

Energy decrease is 0.5C(V12 + V22 - 2Vf2)

Answer

Energy decrease is 0.5C(V1 - V2)2

Answer

Energy decrease is C(V1 - V2)2

Answer

Energy decrease is 2C(V12 - V22)

Question 2

An assembly of charges, +q, -q, +q, -q ........ are placed at distance x = 1m, x = 2m, x = 4m, x = 8m and so on, from the origin, in a plane. The potential at x = 0, due to the charges would be:

Accepted Answer

Finite and non-zero

Answer

Zero

Answer

Indeterminate

Answer

Infinite

Question 3

Two charges Q1 and Q2 C are placed at points R and S. A third charge Q3 C is moved from point R to S along the circular path. Change in potential energy of the charge is:

Accepted Answer

4KQ2Q3

Answer

KQ1Q2Q3

Answer

4KQ1Q2

Answer

2/3 KQ2Q3

Question 4

The figure below shows three circular arcs, each of radius R and total charge as indicated. The net electric potential at the center of curvature is:

Accepted Answer

The net electric potential is proportional to the sum of the charges divided by the radius R.

Answer

The net electric potential is zero due to symmetry.

Answer

The net electric potential depends only on the largest charge.

Answer

The net electric potential is inversely proportional to the sum of the charges.

Question 5

Two points P and Q are maintained at the potentials of 10V and -4V respectively. The work done in moving 100 electrons from P to Q is:

Accepted Answer

2.24 x 10^-16 J

Answer

- 9.60 x 10^-17 J

Answer

9.60 x 10^-17 J

Answer

- 2.24 x 10^-16 J

Question 6

On moving a charge of 2C from a point A where potential is +12V to a point B where potential is -12V, the work done is:

Accepted Answer

-48 J

Answer

+24 J

Answer

-24 J

Answer

48 J

Question 7

Three charges -q, Q and -q are placed at equal distances on a straight line. If the potential energy of the system of three charges is zero, then what is the ratio of Q:q?

Accepted Answer

1 : 4

Answer

1 : 1

Answer

1 : 2

Answer

1 : 3

Question 8

There are 27 drops of a conducting fluid. Each has a radius r and they are charged to a potential V0. These are combined to form a bigger drop. Its potential will be:

Accepted Answer

9V0

Answer

V0

Answer

3V0

Answer

27V0

Question 9

The capacitance of an isolated sphere is increased n times when it is enclosed by an earthed concentric sphere. The ratio of their radii is:

Accepted Answer

Radii ratio is 1:n

Answer

Radii ratio is n:1

Answer

Radii ratio is √n:1

Answer

Radii ratio is 1:√n

Question 10

An electron with a kinetic energy of 100 eV enters the space between the plates of plane capacitor made of two dense metal grids at an angle of 30° with the plates of capacitor and leaves this space at an angle of 45° with the plates. What is the potential difference of the capacitor:

Accepted Answer

50 V

Answer

100 V

Answer

150 V

Answer

200 V

Question 11

The two spherical shells are at large separation. One of them has a radius of 10 cm and has 1.25 µC charge. The other is of 20 cm radius and has a 0.75 µC charge. If they are connected by a conducting wire of negligible capacity, the charge on the shells are:

Accepted Answer

2/3 µC, 4/3 µC

Answer

1 µC, 1 µC

Answer

4/3 µC, 2/3 µC

Answer

0.25 µC, 0.25 µC

Question 12

A capacitor of capacity C1 = 1µF can with stand the maximum voltage V1 = 16 KV while another capacitor C2 = 2µF can with stand the maximum voltage V2 = 4KV. The maximum voltage of capacitance connected in series will be:

Accepted Answer

12 KV

Answer

10 KV

Answer

6 KV

Answer

4 KV

Question 13

In the given circuit, the resistance R has a value that depends on the current. Specifically, R is 20 ohms when I is zero, and the increase in resistance (in ohms) is numerically equal to one-half of the current in amperes. What is the value of current I in the circuit?

Accepted Answer

10 amp

Answer

8.33 amp

Answer

12.5 amp

Answer

18.5 amp

Question 14

An insulated conductor initially free from charge is charged by repeated contacts with a plate which after each contact is replenished to a charge Q. If q is the charge on the conductor after first operation then the maximum charge which can be given to the conductor is:

Accepted Answer

The maximum charge on the conductor is Q(1 - 1/e)

Answer

The maximum charge on the conductor is Q

Answer

The maximum charge on the conductor is 2Q

Answer

The maximum charge on the conductor is q = Q

Question 15

An electric charge 10-3 µC is placed at origin (0, 0). Two points A and B are situated at (√2, √2) and (2, 0) respectively. The potential difference between points A and B will be:

Accepted Answer

Zero

Answer

9 volts

Answer

2 volts

Answer

4.5 volts

Question 16

Two concentric thin metallic spheres of radii R1 and R2 (R1 > R2) bear charges Q1 and Q2 respectively. Then the potential at radius r between R1 and R2 will be 1/(4πε0) times:

Accepted Answer

Option B

Answer

Option A

Answer

Option C

Answer

Option D

Question 17

The charge flowing across the cell on closing the switch is equal to:

Accepted Answer

CV/2

Answer

CV

Answer

2CV

Answer

zero

Question 18

Two charges 1C and -4C exist in air. What is the direction of force?

Accepted Answer

From 1C to -4C

Answer

Away from 1C

Answer

Away from -4C

Answer

From -4C to 1C

Question 19

A point charges 2nC is located at orgin . What is the potential at (1, 0, 0)?

Accepted Answer

18 V

Answer

12 V

Answer

14 V

Answer

16 V

Question 20

What is the dielectric content of the medium if the capacitance of a parallel plate capacitor increases from 40F to 80F on introducing a dielectric medium between the planes?

Accepted Answer

2

Answer

20

Answer

0.5

Answer

5

Free Electrostatics MCQs with Answers