Electrostatic Potential and Capacitance · Question 35

The electrostatic potential on the surface of uniformly charged spherical shell of radius R = 10 cm is 120 V. The potential at the centre of shell, at a distance r = 5 cm from centre, and at a distance r = 15 cm from the centre of the shell respectively, are:

1. 0 V, 120 V, 40 V
2. 120 V, 120 V, 80 V
3. 40 V, 40 V, 80 V
4. 0 V, 0 V, 80 V

Using a battery, a 100 pF capacitor is charged to 60 V and then the battery is removed. After that, a second uncharged capacitor is connected to the first capacitor in parallel. If the final voltage across the second capacitor is 20 V, its capacitance is: (in pF)

1. 600
2. 100
3. 400
4. 200

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). In the light of the above statements, choose the most appropriate answer from the options given below :

1. Both (A) and (R) are correct and (R) is the correct explanation of (A)
2. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
3. (A) is not correct but (R) is correct
4. (A) is correct but (R) is not correct

Two large plane parallel conducting plates are kept 10 cm apart as shown in figure. The potential difference between them is V. The potential difference between the points A and B (shown in the figure) is : [figure]

1. 1 V
2. 14 V
3. 34 V
4. 25 V

Three infinitely long wires with linear charge density are placed along the x-axis, y-axis and z-axis respectively. Which of the following denotes an equipotential surface?

1. (x2 + y2)(y2 + z2)(z2 + x2) = constant
2. xyz = constant
3. xy + yz + zx = constant
4. (x + y)(y + z)(z + x) = constant

Two capacitors C1 and C2 are connected in parallel to a battery. Charge-time graph is shown below for the two capacitors. The energy stored with them are U1 and U2, respectively. Which of the given statements is true? [figure]

1. C2 > C1, U2 > U1
2. C1 > C2, U1 > U2
3. C2 > C1, U2 < U1
4. C1 > C2, U1 < U2

A particle of mass 'm' and charge 'q' is fastened to one end 'A' of a massless string having equilibrium length l, whose other end is fixed at point 'O'. The whole system is placed on a frictionless horizontal plane and is initially at rest. If uniform electric field is switched on along the direction as shown in figure, then the speed of the particle when it crosses the x-axis is [figure]

1. qEl2m
2. qEl4m
3. qElm
4. 2qElm

A parallel plate capacitor of capacitance 1 μF is charged to a potential difference of 20 V. The distance between plates is 1 μm. The energy density between plates of capacitor is :

1. 1.8 103 J/m3
2. 2 102 J/m3
3. 2 10-4 J/m3
4. 1.8 105 J/m3

An electric dipole of dipole moment 6 10-6 C m is placed in uniform electric field of magnitude 106 V/m. Initially, the dipole moment is parallel to electric field. The work that needs to be done on the dipole to make its dipole moment opposite to the field, will be J.