Electrostatic Potential and Capacitance · Question 43

An electric dipole of dipole moment p is aligned parallel to a uniform electric field E. The energy required to rotate the dipole by 90 is

1. p2E
2. pE
3. infinity
4. pE2

A parallel plate capacitor has a uniform electric field E in the space between the plates. If the distance between the plates is d and area of each plate is A, the energy stored in the capacitor is

1. 12 0E2
2. E2Ad 0
3. 12 0E2Ad
4. 0EAd

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

1. 2 10-2 C
2. 3 10-2 C
3. 4 10-2 C
4. 1 10-2 C

An electric dipole of moment p is placed in an electric field of intensity E. The dipole acquires a position such that the axis of the dipole makes an angle with the direction of the field. Assuming the potential energy of the dipole to be zero when = 90 , the torque and the potential energy of the dipole will respectively be

1. pE , -pE
2. pE , -2pE
3. pE , 2pE
4. pE , -pE

Four point charges -Q, -q, 2q and 2Q are placed, one at each corner of the square. The relation between Q and q for which the potential at the centre of the square is zero is

1. Q = -q
2. Q = - 1q
3. Q = q
4. Q = 1q

Three charges, each +q, are placed at the corners of an isosceles triangle ABC of sides BC and AC, 2a. D and E are the mid points of BC and CA. The work done in taking a charge Q from D to E is [figure]

1. 3qQ4 0 a
2. 3qQ8 0 a
3. qQ4 0 a
4. zero

The electric potential V at any point (x, y, z), all in metres in space is given by V = 4x2 volt. The electric field at the point (1, 0, 2) in volt/metre, is

1. 8 along negative X-axis
2. 8 along positive X-axis
3. 16 along negative X-axis
4. 16 along positive X-axis

A parallel plate capacitor has a uniform electric field E in the space between the plates. If the distance between the plates is d and area of each plate is A, the energy stored in the capacitor is

1. 12 0E2
2. E2Ad 0
3. 12 0E2Ad
4. 0EAd

Four electric charges +q, +q, −q and −q are placed at the corners of a square of side 2L (see figure). The electric potential at point A, midway between the two charges +q and +q, is [figure]

1. 14 0 2qL (1 + 5 )
2. 14 0 2qL (1 + 1 5 )
3. 14 0 2qL (1 - 1 5 )
4. zero

Two parallel metal plates having charges +Q and -Q face each other at a certain distance between them. If the plates are now dipped in kerosene oil tank, the electric field between the plates will

1. become zero
2. increase
3. decrease
4. remain same