ANS:
If
you hook up a really cheap dimmer switch, you may notice a strange
buzzing noise. This comes from vibrations in the bulb filament caused by
the chopped-up current coming from the triac.
If you've read How
Electromagnets Work, you know that electricity flowing through a coiled
length of wire generates a substantial magnetic field, and fluctuating
current generates a fluctuating magnetic field. If you've read How Light
Bulbs Work, you know that the filament at the heart of a light bulb is
just a coiled length of wire. It makes sense, then, that this coiled
filament becomes magnetic whenever you pass current through it, and the
magnetic field fluctuates with the AC current.
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