Electric Charges and Fields Easy Questions and Answers | Page - 1

Electric Charges and Fields

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 θ with the direction of the field. Assuming that the potential energy of the dipole to be zero when = 90°, the torque and the potential energy of the dipole will respectively be :

1. p E sin θ, – p E cos θ
1. p E sin θ, –2 p E cos θ
1. p E sin θ, 2 p E cos θ
1. p E cos θ, – p E cos θ

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The torque on the dipole is given as
τ = pE sin θ
The potential energy of the dipole in the electric field is given as
U = – pE cos θ

Correct Option: A

The torque on the dipole is given as
τ = pE sin θ
The potential energy of the dipole in the electric field is given as
U = – pE cos θ

The electric field at a distance 3R from the centre of a charged conducting spherical shell of
2

radius R is E. The electric field at a distance R from the centre of the sphere is
2

1. E
  2
1. zero
1. E
1. E
  2

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Electric field at a point inside a charged conducting spherical shell is zero.

Correct Option: B

Electric field at a point inside a charged conducting spherical shell is zero.

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

1. 8 along positive X-axis
1. 16 along negative X-axis
1. 16 along positive X-axis
1. 8 along negative X-axis

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E^{^→} = - dv î + dv ĵ + dv k̂
dx dy dz

= -8 × î volt/meter
∴ E^{^→} = -8î V / m

Correct Option: D

E^{^→} = - dv î + dv ĵ + dv k̂
dx dy dz

= -8 × î volt/meter
∴ E^{^→} = -8î V / m

The mean free path of electrons in a metal is 4 × 10^–8 m. The electric field which can give on an average 2 eV energy to an electron in the metal will be in units of V/m

1. 5 × 10^–11
1. 8 × 10^–11
1. 5 × 10⁷
1. 8 × 10⁷

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E = V = 2
d 4 × 10^–8

= 0.5 × 10⁸ = 5 × 10⁷ Vm^–1

Correct Option: C

E = V = 2
d 4 × 10^–8

= 0.5 × 10⁸ = 5 × 10⁷ Vm^–1

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. pE²
1. p²E
1. pE
1. infinity

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When electric dipole is aligned parallel θ = 0° and the dipole is rotated by 90° i.e., θ = 90°.
Energy required to rotate the dipole W = U_f – U_i = (–pE cos 90°) – (–pE cos 0°)
= pE.

Correct Option: C

When electric dipole is aligned parallel θ = 0° and the dipole is rotated by 90° i.e., θ = 90°.
Energy required to rotate the dipole W = U_f – U_i = (–pE cos 90°) – (–pE cos 0°)
= pE.