A long straight wire lies along the axis of a circular ring of radius R. The mutual inductance of the wire-ring system is:
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Question

A long straight wire lies along the axis of a circular ring of radius R. The mutual inductance of the wire-ring system is:

G1 Physics · Accepted Answer

The magnetic field of the straight wire is tangential to circles centred on the wire and therefore lies in the plane of the ring. Thus B⃗·dA⃗=0 everywhere over the ring, so magnetic flux through the ring is zero for any wire current. Hence M=0, option D.