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Homework Help: Once upon a light bulb

  1. Mar 2, 2006 #1
    Why does an electric light bulb nearly always burns out just as you turn on the light, but almost never while the light is shining? :confused:
  2. jcsd
  3. Mar 2, 2006 #2


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    The filament is rapidly becoming hotter, and thus rapidly undergoing thermal expansion. During this expansion, any small imperfection may cause it to break.

    Once the bulb is in steady-state, the filament no longer grows hotter, and no longer expands.

    - Warren
  4. Mar 2, 2006 #3


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    The effect is much worse if your bulb is being dimmed by a cheap dimmer switch, because even though the filament is getting less power, it's getting it in a very choppy form that often causes the filament to oscillate and buzz. Better dimmers have a choke and some capacitors to help smooth out the choppy signal coming from the triac.
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