When electric dipole is placed in uniform electric field, its two charges experience equal and opposite forces which cancel each other and hence net force on electric dipole in uniform electric field is zero. However, these forces are not collinear, so they give rise to some torque on the dipole. Since net force on electric dipole in uniform electric field is zero. so, no work is done in moving the electric dipole in uniform electric field. However, some work is done in rotating the dipole against the torque acting on it. 

 

The dipole moment of a dipole in a uniform external field $\overrightarrow{E}\text{ is }\overrightarrow{P}$ . Then the torque $\overrightarrow{\tau }$ acting on the dipole is