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A long straight wire is placed along the axis of a circular ring of radius R. What is the mutual inductance of this arrangement?
- mu0*R/2
- mu0*pi*R/2
- mu0/2
- 0
Correct answer: 0
Solution
When the straight wire lies along the axis of the ring, the magnetic field lines of the wire are circles concentric with (and in the plane perpendicular to) the wire. The plane of the ring contains the wire (the wire is along the axis), so the field is everywhere parallel to the plane of the ring and the net flux linked is zero. Therefore the mutual inductance is zero.
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