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P. 4032. A uniform metal disc is rotated about an axle, which goes through its centre and which is perpendicular to it. The disc is in uniform magnetic field, the magnetic induction is parallel to the axis of rotation. Usually electromotive force is induced between the rim of the disc and its axle. Though if we are clever we can rotate the disc in such way that no e.m.f. induced between the rim and the axle. How should we rotate the disc if the magnetic induction at the disc is 10-8 T.

(5 points)