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Homework Help: Electromotive Force

  1. Mar 19, 2009 #1
    1. The problem statement, all variables and given/known data

    A power supplyused in a lab has an emf of 5000V. However, when a voltmeter of resistance 20kohm is connected to the terminal of the power supply, a reading of only 24V is obtained. Explain this conservation and calculate any necessary quantity.

    3. The attempt at a solution

    Not really sure where to go with this. I think it has something to do with internal resistance and such but... not really sure. Could someone at least point me in the right direction?

    Thank you.
  2. jcsd
  3. Mar 19, 2009 #2


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    Homework Helper

    Maybe start by drawing a circuit diagram.

    You have a box that nominally has 5000V.

    But when you effectively put a 20KΩ load across it, it only reads 25V.

    So what you apparently have is some kind of voltage divider.

    Perhaps you want to consider some internal resistance?
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