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Voltage effects on power dissipated

  1. May 23, 2013 #1
    Trying to find the relationship between voltage and power across a resistive something.

    Using a lightbulb if the bulb was rated at 100W when 140 Volts is used, what would happen to the power if the voltage was doubled? (assuming the light bulb doesn't explode)
  2. jcsd
  3. May 23, 2013 #2


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    Staff: Mentor

    Welcome to PF.

    If the light bulb doesn't explode, it obeys V=IR and P=VI.
  4. May 23, 2013 #3
    Light bulbs aren't aware of Ohm's law.
    The current would probably go up between 5% and 100%. Current would depend on rating of light bulb.
    Unless of course the light bulb used a carbon filament, then the current would more than double.
  5. May 24, 2013 #4
    Other then electronics 101.....Watts = V^2/R ..... but lightbulbs are specifcally made to give off light - not be resistors.

    What C-P is alluding to is that the element of the light bulb is a resistor - but the resistance varies greatly with temperature. Tungsten has a Positive Temp Coefficent - as the temp goes up the resistance goes up. A carbon element has a negative TC (as do Diodes ) so as the temp goes up the resistance goes down -

    Precision resistors usually have a specific rating for this TCR.

    Soooo - the better question would be - how doe the resistance of a light bulb vary over voltage - that totally depends on the lightbulb!
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