question_answer

An infinitely long current carrying wire and a small current carrying loop are in the plane of the paper as shown. The radius of the loop is a and distance of its centre from the wire is \[d\left( d>>a \right)\]. If the loop applies a force F on the wire then: [JEE Main 09-Jan-2019 Morning]

A)             \[F\propto \left( \frac{{{a}^{2}}}{{{d}^{3}}} \right)\]

B) \[F\propto \left( \frac{a}{d} \right)\]

C)             \[F\,\,=\,\,0\]

D) \[F\propto {{\left( \frac{a}{d} \right)}^{2}}\]

Correct Answer: D

Solution :

[d]

work done by magnetic force = fdx

dx