ElectroMagnetic InductionHard
Question
A and B are two metallic rings placed at opposite sides of an infinitely long straight conducting wire as shown. If current in the wire is slowly decreased, the direction of induced current will be :


Options
A.clockwise in A and anticlockwise in B
B.anticlockwise in A and clockwise in B
C.clockwise in both A and B
D.anticlockwise in both A & B
Solution
The field at A and B are out of the paper and inside the paper respectively.

As the current in the straight wire decreases the field also decreases.
For B :

The change in the magnetic field which causes induced current
is along (+)z direction.
Hence, induced emf and hence current should be such as to oppose this change
Hence, induced emf should be along − z direction which results in a clockwise current in ′B′. Similarly, there will be anticlockwise current in ′A′. Hence (B).

As the current in the straight wire decreases the field also decreases.
For B :

The change in the magnetic field which causes induced current
Hence, induced emf and hence current should be such as to oppose this change
Hence, induced emf should be along − z direction which results in a clockwise current in ′B′. Similarly, there will be anticlockwise current in ′A′. Hence (B).
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