Question

Derive an expression for torque acting on a dipole placed in a uniform Electric-field.

Answer 1

Force acting on the +ve charge \(F_1=E_q\)

in the direction of field.

Force acting on the -ve charge \(F_2=E_q\)

in opposite to the direction of field.

\(|F_1|=|F_2|\)

These two equal and unlike parallel forces constitute a couple which tends to rotate the dipole in the direction of the field.

The moment of the couple or torque acting on the dipole is given by