A copper disk with radius r0=20 cm rotates in a vertical plane at 3000 rpm. A sensitive galvanometer is connected by one terminal to the axis of the disk, the other - through a mercury contact - to the outer edge of the disk (Fig. 31.2 a). Determine the potential difference. Will the direction of deflection of the galvanometer needle change when the direction of rotation of the disk changes? The Earth's magnetic field is compensated.

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