Question

A molecule with 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 antiparallel to the field, the work required to be done by an external agency is:

• A. –2pE
• B. –pE
• C. pE
• D. 2pE

Answer 1

The correct option is D

2pE

${\theta }_1=0$ [Initially dipole sets parallel to electric field]
${\theta }_2={180}^{\circ }$
Work done $=PE[cos{\theta }_1-cos{\theta }_2]$
$=PE[cos{0}^{\circ }-cos{180}^{\circ }]$
$=PE[1–(–1\left)\right]$
$W=2PE$