Question

An electric dipole of moment vector s placed in a uniform electric field of intensity vector at an angle theta with respect to the field. The direction of the torque is ………………..

(a) along the direction of vector
(b) opposite to the direction of vector
(c) along the direction of vector
(d) perpendicular to the plane containing vector and vector.​

Answer 1

Answer:

The dipole experiences a torque pEsinθ tending to bring itself back in the direction of field.

Therefore, on being released (i.e., rotated) the dipole oscillates about an axis through its centre of mass and perpendicular to the field. If I is the moment of inertia of the dipole about the axis of rotation, then the equation of motion is I.d  

2

θ/dt  

2

=−pEsinθ

Foe small amplitude sinθ≈θ

Thus d  

2

θ/dt  

2

=−(pE/I).θ=−ω  

2

θ

where

ω=  

(pE/I)

​

 

This is a S.H.M whose period of oscillation is

T=2π  

(I/PE)

​

Explanation: