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Light bulb wattage

  1. Jan 21, 2004 #1
    How may watts does a 60-watt light bulb use in three hours?

  2. jcsd
  3. Jan 21, 2004 #2


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    Watts are a measure of power. Power is a rate of energy usage. "How many watts used in an hour?", is a nonsensical question.

    Sensible questions would be:

    -How many kilowatt-hours does a 60 watt bulb use in 3 hours?

    -How many joules does a 60 watt bulb use in 3 hours?

    Keeping in mind that a watt is 1 joule per second.

  4. Jan 21, 2004 #3
    How many kilowatt-hours does a 60 watt bulb use in 3 hours?

    how can i convert that to amps?
  5. Jan 21, 2004 #4


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    You can't.
  6. Jan 21, 2004 #5


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    60 watts for 3 hours is 60 * 3 = 180 watt-hours. That's the same as 0.180 kilowatt-hours.

    Your next question, "how do I convert that [kilowatt-hours] into amps?" is as non-sensical as the first question.

    - Warren
  7. Jan 21, 2004 #6


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    Amps = unit of current = rate of change of charge.

    Volts = unit of electric potential

    Joules = unit of energy.

    Watt = unit of power = rate of change of energy

    Kilowatt-Hours = Non-SI unit of energy

    You cannot calculate current from power unless you know the voltage, or the resistance.
  8. Jan 22, 2004 #7
    ya, i'm confused
  9. Jan 23, 2004 #8


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    Watts and amps are both rates. They both stay constant and do not change with time.

    To find the amps, divide by the watts by 120.
  10. Jan 23, 2004 #9


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    Uh... hmm. This is true (as a simplification) in this case, but is not always true.

    Not neccessarily. Depends on the country.
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