In modern music, electricity is often used to send sound over long
distances or to make it louder. The simplest way of converting sound to electricity
is to use a microphone. This is simply a diaphragm
connected to a variable resistor which changes the shape of the electrical wave to match
that of the sound wave. The electrical wave can now travel down a length of wire at
nearly the speed of light - much faster than sound travels - and be output at the other
end by a speaker. A speaker is simply the opposite of a microphone. The
varying voltage of the electricity causes magnets in the speaker to move and these in turn
move a paper cone making air particles vibrate.
Mains electricity can be considered a wave. As such, it can
always be made to produce a sound. The electricity that is supplied to your house is
at a frequency of 50Hz. This makes a very low pitch sound. It also means that
your lights are varying at this frequency, so they are effectively flashing on and off
very fast so your eye cannot see it.