When an electric dipole is placed in a uniform electric field making angle `theta` with electric field, it experiences a torque `tau`. Calculate the minimum work donein changing the orientation to `2 theta`.

Explanation

`tau = pE sin theta `
`rArr pE = (tau)/(sin theta)`
`W = DeltaU = - pE cos theta_(2) + pE cos theta_(1)`
`rArr W = p E [ cos theta - cos 2 theta]`
`(because theta_(1) = theta, theta_(2) = 2theta)`
`rArr W = (tau)/(sin theta) [ cos theta - cos 2 theta]`