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General
Easy
Question
A thin non conducting disc of radius R is rotating clockwise (see figure) with an angular velocity w about its central axis, which is perpendicular to its plane. Both its surfaces carry +ve charges of uniform surface density. Half the disc is in a region of a uniform, unidirectional magnetic field B parallel to the plane of the disc, as shown. Then,
- The net torque on the disc is zero.
- The net torque vector on the disc is directed leftwards.
- The net torque vector on the disc is directed rightwards.
- The net torque vector on the disc is parallel to B.
The correct answer is: The net torque vector on the disc is directed leftwards.
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