Question

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 (d >> a). If the loop applies a force F on the wire then : (A) F = 0 (B) F ∝ (a/d)
(C) F ∝
(a²/d³)
(D) F ∝ (a/d)²
[JEE Main 2019]

Answer 1

Answer:

A

Explanation:

Answer 2

Thus the force applied by the loop is F ∝ a^2 / d^2

Option (D) is correct.

Explanation:

Equivalent dipole of given loop

F = m.dB / dr

Now, dB / dx = d / dx ( μoI / 2πx )

dB / dx ∝ 1/x^2

Therefore F ∝ M / x^2 [ M = NIA]

F ∝ a^2 / d^2

Thus the force applied by the loop is F ∝ a^2 / d^2