Here's a microphone fun fact tied to a bit of music history. Microphones basically work in the same fashion as a loudspeaker, only in reverse (sound wave -> electrical signal and visa versa). It uses electromagnetic induction - sound waves move a magnet surrounded by a coil, producing a current.
But anyway, when recording
Paperback Writer,
Geoff Emerick (the Beatles' recording engineer) actually
used a loudspeaker wired in reverse instead of a microphone to record the low end of Paul's bass better. That's why that song has such a distinct bass line. Fun fact of the day!