A uniform magnetic field B exists in circular region of radius R as shown which is decreasing with time at a constant rate. There is a concentric wooden ring which have uniformly distributed charge Q

Question

A uniform magnetic field B exists in circular region of radius R as shown which is decreasing with time at a constant rate. There is a concentric wooden ring which have uniformly distributed charge Q and radius 2R and another concentric uncharged copper ring of radius 3R, then select incorrect alternative. (Assume rings are placed on frictionless surface) :-

TestHub · Accepted Answer

For r > R the induced field is E = 2 r R 2 ​ ​ d t d B ​ ​ ∝ r 1 ​ . So E at the wooden ring (2R) exceeds that at the copper ring (3R) - (B) is correct and (C) is INCORRECT. No current in the insulator (A correct); the field exerts torque on the charged wooden ring, so it rotates (D correct). Answer (C).

Physics - EMI/AC Question with Solution | TestHub

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JEE Advanced 2027 (Class 12)