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EMF, Power Output, and Terminal Voltage

  1. May 12, 2009 #1


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    1. The problem statement, all variables and given/known data
    A battery supplies a steady current of 5.6 A for 21s. During this time 1410J of chemical energy is transformed into electric energy, but 560J of this electric energy is transformed into heat energy inside the battery.

    a) What is the emf of the battery?

    b) What is the total power output of the battery?

    c) What is the terminal voltage fo the battery?

    2. Relevant equations
    emf= Ve + V
    P= VI or P= V2/R
    Ve= emf - V or Ve= emf- Ir

    3. The attempt at a solution
    My attempt to find the emf was (1410J)/(21s) and to multiply that by (1.6 X 10-19), since the emf is the "amount of chemical energy transformed to electric potential energy per coulomb of charge." However, I am not sure if I am to include or minus the 560J from the 1410J.
    Then to find the power output, I am assuming that you would use P=VI, where the V is the emf.
    After that, I don't know how to find the terminal voltage.
  2. jcsd
  3. May 12, 2009 #2
    Looks like you just stuck the charge of a single electron in there. You know P=VI, and you know power is just a rate of energy, P = E/t. That means you have everything you need.
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