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Homework Help: Electricity help

  1. Mar 10, 2007 #1

    CathyLou

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    Hiya.

    I'm really struggling with the following electricity questions and so any help would be very much appreciated.

    How many available electrons are there in a 25 Ah battery?

    How many electrons pass through a 240 V mains shower heater of 8 kW if it is on for 5 minutes?

    Thank you.

    Cathy
     
    CathyLou, Mar 10, 2007
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  3. Mar 10, 2007 #2

    rsk

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    You have to find the charge moving/transferring in each case first then convert this knowing the charge on an electron.

    So, you need the formula that links charge, current and time (and watch out, your battery is given in Amps Hours and you'll need it in seconds)
     
    rsk, Mar 10, 2007
  4. Mar 10, 2007 #3

    CathyLou

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    Thanks for replying.

    To convert the battery from Amp Hours to seconds, do I just divide 25 by 60?

    I know that I = Q / t and that the charge on an electron is 1.6 x 10^-1, but I'm still not sure how to get an answer to the first question.

    Cathy
     
    CathyLou, Mar 10, 2007
  5. Mar 10, 2007 #4

    rsk

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    No, I think you'd multiply by 60x60.

    I think 25Ah means it can give 25 amps for 1 hour (or 1 amp for 25 hours or any number of other combinations) so it will give 25 amps for 60x60 seconds.

    That will give you the total charge available - and since you know the charge on each electron, just divide by that to find out how many electrons.
     
    rsk, Mar 10, 2007
  6. Mar 11, 2007 #5

    CathyLou

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    Okay. Thanks for your help!
     
    CathyLou, Mar 11, 2007
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