Explain the force acting on electric dipole when it is placed parallel or anti parallel to electric field.

Explanation

When `vecp` is parallel to `vecE` or antiparallel to `vecE` . In either case, the net torque is zero, but there is a net force on the dipole if `vecE` is not uniform.

It is easily seen that when `vecp` is parallel to `vecE` , the dipole has a net force in the direction of increasing field.
When `vecp` is antiparallel to `vecE` , the net force on the dipole is in the direction of decreasing filed.
In general, the force depends on the orientation of `vecP` with respect to `vecE`.