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DC light bulb on AC circuit

  1. Feb 11, 2009 #1
    Assuming equal voltage, will it burn-out an AC light bulb if I put it on a DC circuit?
  2. jcsd
  3. Feb 11, 2009 #2


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    What do you mean by equal voltage?

    Equal RMS: probably not.

    Equal peak: depends on how hot the filament gets

    Equal average: won't turn on.

    HINT: how is power calculated in an AC circuit?
  4. Feb 11, 2009 #3


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    RMS volts, yes. Since a lightbulb is basically a resistor it should be fine. RMS AC is the same voltage that it takes to make the same amount of heat in a resistor driven with the same DC voltage.
  5. Feb 11, 2009 #4
    Ohm's Law: volts (E) = amps (I) * ohms (R)
    Watts Law: watts (P) = amps (I) * volts (E).
    A useful derivation is: P = (I^2) * R = current squared * resistance

    Let's try a 100-watt lightbulb. And 120 VAC.

    AC: 100 watts = .833^2 amps * 144 ohms
    120 volts = .833 amps * 144 ohms

    I believe your previous correspondent, that a lightbulb is a resistor. So, maybe we know from above that a 100-watt lightbulb is a 144-ohm resistor. Let's try with a 12VDC car battery.

    DC: 12 volts = .0833 amps * 144 ohms
    1 watts = .0833^2 amps * 144 ohms

    Does this show that the lightbulb will not burn out? Does it also show that the bulb won't dissipate enough power to glow?
  6. Feb 11, 2009 #5


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    Who said anything about using the light bulb on 12 volts? The question was whether it was AC or DC.
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