Question

A molecule with a dipole moment p is placed in an electric field of strength E. Initially the dipole is aligned parallel to the field. If the dipole is to be rotated to be anti-parallel to the field, the work required to be done by an external agency is

• A. – 2pE
• B. – pE
• C. pE
• D. 2pE

Answer 1

Answer: (D)

2pE

Answer 2

$W = PE(1 - \cos\theta)$ here θ = 180^o

∴ W = $PE(1 - \cos 180^{o})$ = $PE\lbrack 1 - ( - 1)\rbrack = 2PE$