Electric Charges and Fields · Question 3

An electric dipole is placed at an angle of 30 with an electric field of intensity 2 105 N C-1. It experiences a torque equal to 4 N m. Calculate the magnitude of charge on the dipole, if the dipole length is 2 cm.

1. 6 mC
2. 4 mC
3. 2 mC
4. 8 mC

If s E dS = 0 over a surface, then:

1. the magnitude of electric field on the surface is constant.
2. all the charges must necessarily be inside the surface.
3. the electric field inside the surface is necessarily uniform.
4. the number of flux lines entering the surface must be equal to the number of flux lines leaving it.

Two point charges -q and +q are placed at a distance of L, as shown in the figure. [figure] The magnitude of electric field intensity at a distance R (R >> L) varies as:

1. 1R2
2. 1R3
3. 1R4
4. 1R6

The ratio of Coulomb's electrostatic force to the gravitational force between an electron and a proton separated by some distance is 2.4 1039. The ratio of the proportionality constant, K = 14 0 to the gravitational constant G is nearly (Given that the charge of the proton and electron each = 1.6 10-19 C, the mass of the electron = 9.11 10-31 kg, the mass of the proton = 1.67 10-27 kg) :

1. 10
2. 1020
3. 1030
4. 1040

A dipole is placed in an electric field as shown. In which direction will it move? [figure]

1. towards the right as its potential energy will increase.
2. towards the left as its potential energy will increase.
3. towards the right as its potential energy will decrease.
4. towards the left as its potential energy will decrease.

A spherical conductor of radius 10 cm has a charge of 3.2 10-7 C distributed uniformly. What is the magnitude of electric field at a point 15 cm from the centre of the sphere? ( 14 0 = 9 109 N m2/C2 )

1. 1.28 105 N/C
2. 1.28 106 N/C
3. 1.28 107 N/C
4. 1.28 104 N/C

A hollow metal sphere of radius R is uniformly charged. The electric field due to the sphere at a distance r from the centre :

1. zero as r increases for r < R, decreases as r increases for r > R
2. zero as r increases for r < R, increases as r increases for r > R.
3. decreases as r increases for r < R and for r > R.
4. increases as r increases for r < R and for r > R.

Two point charges A and B, having charges +Q and -Q respectively, are placed at certain distance apart and force acting between them is F. If 25% charge of A is transferred to B, then force between the charges becomes :

1. F
2. 16F9
3. 9F16
4. 4F3

Two parallel infinite line charges with linear charge densities + C/m and - C/m are placed at a distance of 2R in free space. What is the electric field mid-way between the two line charges?

1. 2 0R N/C
2. zero
3. 0R N/C
4. 2 0R N/C

An electron falls from rest through a vertical distance h in a uniform and vertically upward directed electric field E. The direction of electric field is now reversed, keeping its magnitude the same. A proton is allowed to fall from rest in it through the same vertical distance h. The time of fall of the electron, in comparison to the time of fall of the proton is

1. smaller
2. 5 times greater
3. 10 times greater
4. equal