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Homework Help: Average Energy Use

  1. Apr 18, 2005 #1
    I'm helping a friend with this question and wanted to make sure I was doing it correctly...

    Suppose your local power company charges 6.3 cents per kilowatt hour and your most recent bill came to $27.00. How much energy, on average, did you use (in Joules) per second last month? Assume that the billing period covered 30 days.

    $27.00/($0.063/kilowatt hour) = 428.571428... kilowatt hours

    428.57... * (3.6 x 10^6) = (1.5428571428571 * 10^9 Joules)/month = M

    M / (30 * 24 * 60 * 60) = 595.23809523808 Joules/second

    Thanks for the help!
     
  2. jcsd
  3. Apr 18, 2005 #2

    dextercioby

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    It's okay.U may wanna learn the concept of significant figures,though...:rolleyes:

    Daniel.
     
  4. Apr 18, 2005 #3
    Thank you, Daniel...Sorry about the sigdigs.
    I know these are just silly conversions for the most part, but could someone please verify the second half of the question as well?

    Now pretend that roughly 2/3 of the energy usage last month was a result of a 120 V air-conditioner, how many Coulombs of charge per second did that air-conditioner draw?

    595.24... * 2/3 = 396.83...J/s
    V = J/C
    120 Volts = (396.83... J/s) / (Coulombs/s)
    3.21 Coulombs/second
     
  5. Apr 18, 2005 #4

    dextercioby

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    It looks okay to me.


    Daniel.
     
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