A circular metallic disc is placed with its plane perpendicular to a uniform magnetic field of flux density B. The disc has a radius of 0.4 m and is rotated at 7 revolutions per second about an axis through its center perpendicular to its plane. The e.m.f between the center and the rim of the disc is balanced by the potential difference across a 10 Ω resistor when carrying a current of 1 mA. Calculate the magnitude of the magnetic field strength.

A circular metallic disc is placed with its plane perpendicular to a uniform magnetic field of flux density B. The disc has a radius of 0.4 m and is rotated at 7 revolutions per second about an axis through its center perpendicular to its plane. The e.m.f between the center and the rim of the disc is balanced by the potential difference across a 10 Ω resistor when carrying a current of 1 mA. Calculate the magnitude of the magnetic field strength.

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