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Resistors question

  1. Jan 21, 2009 #1
    1. A battery is manufactured to have and emf of 24V, but the terminal voltage is only 22V when the battery is connected across a 7.5ohm resistor...what is the internal resistance of the battery?




    3. Ok I have the answer already which is .68ohm...but I can't find a way to get to it. At first I tried V=IR or 24=I*7.5 and then plugged that answer into the same equation but with the voltage of 22. I also tried the opposite way. That answer didn't work.

    I also tried subtracting the volts from each other to get .27R. Can someone please tell me what I am doing wrong?
     
  2. jcsd
  3. Jan 21, 2009 #2

    Doc Al

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    Staff: Mentor

    Answer these questions:
    What's the voltage drop across the internal resistance?
    What's the current through the circuit?
    Combine these two answers to find the internal resistance.
     
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