**Q. An electric dipole of moment p is placed parallel to the uniform electric field. The amount of work done in rotating the dipole by 90 ^{0} is-**(i) 2pE

(ii) pE

(iii) pE/2

(iv) Zero

**Answer: (ii) pE **

W = pE ( cosθ_{1}– cosθ_{2} )

θ_{1} =0°

θ_{2} = 90°

W = pE (cos 0° – cos 90°)

W = pE (1 – 0) = pE