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Q & A: buzzing bulbs

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Most recent answer: 10/22/2007
Q:
Why does electricity make a buzzing sound light a light bulb?
- mike
A:
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.

Mike W.

(published on 10/22/2007)

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