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Transistor radio/kWh problem

  1. Jan 24, 2009 #1
    **Transistor radio/kWh problem**

    A transistor radio operates by means of a 10.0 V battery that supplies it with a 48 mA current.

    (a) If the cost of the battery is $0.55 and it lasts for 300 h, what is the cost per kWh to operate the radio in this manner?
    3.819 dollars/kWh


    (b) The same radio, by means of a converter, is plugged into a household circuit by a homeowner who pays 6¢ per kWh. What does it now cost to operate the radio for 300 h?
    ??? cents

    I got Question A but I have tried everything on Question B and I do not understand what I am doing wrong. For some reason, I think it is easier than what I'm trying to do.

    Please help!
     
  2. jcsd
  3. Jan 24, 2009 #2
    Re: **Transistor radio/kWh problem**

    Work out the number of kilowatt hours and multiply by 6.Note that the question gives the current in mA and not A and note also the the power must be expressed in kW and not W.
     
  4. Jan 24, 2009 #3
    Re: **Transistor radio/kWh problem**

    So if one kWh = 3.6E6 J, and the total energy is 518,400 J..

    (3.6E6)/(518400) = 6.9444

    --> (6.9444)(6) = 41.666

    Is 41.666 cents the answer? I only have two more tries left and I don't want to get it wrong. I'm not sure if those are the correct unit conversions
     
  5. Jan 24, 2009 #4
    Re: **Transistor radio/kWh problem**

    W=10*48/1000
    kW=above/1000
    kWh=above*300
    cost=above*6
     
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