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Why does electricity make a buzzing sound light a light bulb?
Probably the buzz you hear is mostly at a frequency of 120 Hz if you
live in the U.S. and 100 Hz if you live in, say, England. The reason is
that the electrcity supplied in each place is ac- it goes back and
forth at a frequency used throughout that power grid. In the U.S. the
frequency is 60 Hz, and in Europe it's 50 Hz.
Why the buzzing at twice the line frequency? In a bulb, when the
current is flowing (it doesn't matter which way) extra energy is being
poured in. Things expand a little bit. Then they contract when the
current is very small, then expand agin when it flows the other way.
They can also pull together when there's an electrical voltage between
them and relax back when there isn't. The net effect is to set up
vibrations at twice the frequency of the current, because either sign
of current makes the same sign of effect on the sound.
Usually, fluorescent bulbs buzz more than incandescent ones. That's
partly because the filament in incandescent bulbs doesn't have time to
heat up or cool down much in one electrical cycle.
(republished on 08/02/06)
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