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A microphone is similar in set-up to the speaker of Fig. 9.9, except that a current is not sent through the wire loop. Instead, sound waves enter the microphone, which cause the microphone to vibrate back and forth. This subsequently causes the wire loops to oscillate, and the magnetic field through the plane of the loops subsequently changes, inducing a current in the wires. In this way sound or wave energy is converted into electrical energy.