Question

An electric dipole is fixed at the origin of coordinates. Its moment is directed in the positive x-direction. A positive charge is moved from the point (r, 0) to the point (–r, 0) by an external agent. In this process, the work done by the agent is -

• A. Positive and inversely proportional to r
• B. Positive and inversely proportional to r²
• C. Negative and inversely proportional to r
• D. Negative and inversely proportional to r²

Answer 1

Answer: (D)

Negative and inversely proportional to r²

Answer 2

The potential due to the dipole is positive at

A(r, 0) and negative at B(–r, 0). Also this potential is inversely proportional to r². Work is done by agent is also inversely proportional to r² W_{ext. A ® B} = q (V_B – V_A) = –ve

↓ ↓

–ve +ve