NCERT Solutions for class 12 Physics | Chapter 2 - Electrostatic Potential Capacitance

Questions
1 What is the number of electrons in 100 g water?
A 3.35 × 1024
B 3.35 × 1025
C 6.02 × 1023
D None of these

Answer:3.35 × 1024
2 The electric potential of earth is taken as:
A zero
B infinity
C unity
D None of these

Answer:zero

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3 Which of the following statement is true?
A Electrostatic force is a conservative force.
B Potential at a point is the work done per unit charge in bringing a charge from any point to infinity.
C Electrostatic force is non-conservative
D Potential is the productof charge and work.

Answer:Electrostatic force is a conservative force.
4 A capacitor is charged by using a battery which is then disconnected. A dielectric slab then slipped between the plates, which results in
A reduction of charge on the plates and increase of potential difference across the plates.
B increase in the potential difference across the plate, reduction in stored energy, but no change in the charge on the plates.
C decrease in the potential difference across the plates, reduction in the stored energy, but no change in the charge on the plates.
D none of these

Answer:decrease in the potential difference across the plates, reduction in the stored energy, but no change in the charge on the plates.
5 The work done in bringing a unit positive charge from infinite distance to a point at distance x from a positive charge Q is W. Then the potential at that point is
A WQ/x
B W
C W/x
D WQ

Answer:W
6 Acapacitor of 4 pF is connected as shown in the circuit. The internal resistance of the battery is 0.5

Q. The amount of charge on the capacitor plates will be

Electrostatic Potential and Capacitance

A 0
B 4
C 16 μC
D 8 μC

Answer:8 μC
7 Two metal plates form a parallel plate capacitor. The distance between the plates is d. A metal sheet of thickness d/2 and of the same area is introduced between the plates. What is the ratio of the capacitance in the two cases?
A 2 : 1
B 3 : 1
C 2 : 1
D 5 : 1

Answer:2 : 1
8 Three charges Q, +q and +q are placed at the vertices of an equilateral triangle of side l as shown in the figure. If the net electrostatic energy of the system is zero, then Q is equal to

Electrostatic Potential and Capacitance

A -q
B +q
C zero
D –q/2

Answer:–q/2
9 A parallel plate condenser is connected with the terminals of a battery. The distance between the plates is 6mm. If a glass plate (dielectric constant K = 9) of 4.5 mm is introduced between them, then the capacity will become
A 2 times.
B the same.
C 3 times.
D 4 times.

Answer:3 times.
10 The radii of two metallic spheres A and B are r1 and r2 respectively (r1 > r2). They are connected by a thin wire and the system is given a certain charge. The charge will be greater
A on the surface of the sphere B.
B on the surface of the sphere A.
C equal on both.
D zero on both.

Answer:on the surface of the sphere A.
11 64 drops each having the capacity C and potential V are combined to form a big drop. If the charge on the small drop is q, then the charge on the big drop will be
A 2q
B 4q
C 16q
D 64q

Answer:64q
12 Two small spheres each carrying a charge q are placed r metre apart. If one of the spheres is taken around the other one in a circular path of radius r, the work done will be equal to
A force between them × r
B force between them × 2πr
C force between them/2πr
D zero

Answer:zero
13 If a unit positive charge is taken from one point to another over an equipotential surface, then
A work is done on the charge.
B work is done by the charge.
C work done is constant.
D no work is done.

Answer:no work is done.
14 The electrostatic force between the metal plates of an isolated parallel plate capacitor C having a charge Q and area A, is
A proportional to the square root of the distance between the plates.
B linearly proportional to the distance between the plates.
C independent of the distance between the plates.
D inversely proportional to the distance between the plates.

Answer:independent of the distance between the plates.
15 Which of the following options are correct? If a conductor has a potential V 4- 0 and there are no charges anywhere else outside, then
A there must not be charges on the surface or inside itself.
B there cannot be any charge in the body of the conductor.
C there must be charges only on the surface.
D there must be charges inside the surface.

Answer:there cannot be any charge in the body of the conductor.
16 Which of the following options is correct? In a region of constant potential
A the electric field is uniform.
B the electric field is zero.
C there can be charge inside the regiofi.
D the electric field shall necessarily change if a charge is placed outside the region.

Answer:the electric field is zero.
17 v Figure shows the electric lines of force emerging from a charged body. If the electric field at A and B are EA and EB respectively and if the displacement between A and B is r then

Electrostatic Potential and Capacitance

A EA > EB
B EA < EB
C EA = EB/r
D EA = EB /r²

Answer:EA > EB
18 A conductor with a positive charge
A is always at +ve potential.
B is always at zero potential.
C is always at negative potential.
D may be at +ve, zero or -ve potential.

Answer:may be at +ve, zero or -ve potential.
19 A capacitor is charged by a battery. The battery is removed and another identical uncharged capacitor is connected in parallel. The total electrostatic energy of resulting system
A increases by a factor of 4.
B decreases by a factor of 2.
C remains the same.
D increases by a factor of 2.

Answer:decreases by a factor of 2.
20 A hollow metal sphere of radius 5 cm is charged so that the potential on its surface is 10 V. The potential at the centre of the sphere is
A 0 V
B 10 V
C Same as at point 5 cm away from the surface
D Same as at point 25 cm away from the surface

Answer:10 V

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