Torque On An Electric Dipole In A Uniform Electric Field - Practice Questions & MCQ

Net Force-  

When a dipole is kept in a uniform electric field. The net force experienced by the dipole is zero as shown in the below figure.

I.e 

Hence dipole will not make any linear motion.

Torque on dipole-

Net torque about the center of dipole is given as 

Using    we get 

 So  

• The direction of the torque is normal to the plane containing dipole moment P and electric field E and is governed by right-hand screw rule.
• If Dipole is parallel to E the torque is Zero. I.e        (This is the position of stable equilibrium of dipole)

• Torque is maximum when Dipole is perpendicular to E. I.e               

Oscillation of dipole -If a dipole experiencing a torque in an electric field is allowed to rotate, then it will rotate to align itself to the Electric field. But when it reaches along the direction of E the torque becomes zero. But due to inertia, it overshoots this equilibrium condition and then starts oscillating about this mean position.

The time period of this oscillation is given as 

where I= moment of inertia of dipole about the axis passing through its center and perpendicular to its length.

Dipole in Non-Uniform Electric field- In case the Electric field is non-uniform, the magnitude of the force on +q and –q will be different. So    and At the same time due to a couple of forces acting, a torque will also be acting on it.