AC Electric Circuits
Explain how a moving-coil, or dynamic microphone works. Identify how the principle of electromagnetic induction is put to practical use in this device.
Explain how a crystal microphone works. Identify how the principle of piezoelectricity is put to practical use in this device.
Follow-up question: characterize the typical output impedance of this microphone type. Is it generally considered a low-impedance or a high-impedance 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 rapidly-varying capacitance, employing the mathematical relationship between charge (Q), capacitance (C) and voltage (V).
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