A moving magnet microphone is similar to a moving coil microphone (Fig. 20.15) except that the coil is stationary and the magnet is attached to the diaphragm, which moves in response to sound waves in the air. If, in response to a sound wave, the magnet move according to x(t) = A sin ωt, the induced emf in the coil would be (approximately) proportional to which of these?

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(a) sin cot (b) cos wt (c) sin 2wt (d) cos 2wt oce