Microphones
AC Electric Circuits
Explain how a crystal microphone works. Identify how the principle of piezoelectricity is put to practical use in this device.
Followup question: characterize the typical output impedance of this microphone type. Is it generally considered a lowimpedance or a highimpedance type of microphone? Why do you think this is?
The basic circuit for an unamplified capacitor microphone looks like this:

Vibrations in the air cause one metal plate to vibrate next to a stationary metal plate, rapidly changing the capacitance between the two plates. Explain how this simple circuit generates an AC voltage from this rapidlyvarying capacitance, employing the mathematical relationship between charge (Q), capacitance (C) and voltage (V).
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