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Homework Help: Terminal Voltage

  1. Dec 30, 2013 #1
    1. The problem statement, all variables and given/known data

    (a) Find the terminal voltage of a 12.0-V motorcycle battery having a 0.520 Ω internal resistance, if it is being charged by a current of 11.7 A.

    (b) What is the output voltage of the battery charger?

    2. Relevant equations

    ΔV = ε - IR
    Vterminal = ε - IR

    3. The attempt at a solution

    ΔV = 12 - (11.7*0.52) = 5.916 = Vterminal

    This is incorrect. WebAssign also returned this information:

    "What is the sign of the current if it is flowing into the positive terminal of the battery? How is terminal voltage related to the internal resistance and battery emf?"

    So I made it negative and submitted the response: -5.916

    Still wrong. What am I missing?
  2. jcsd
  3. Dec 30, 2013 #2


    User Avatar

    Staff: Mentor

    You have an external voltage (the "charger") supplying a given current into the battery (which includes an internal resistance). Draw the circuit and pencil in the current and potential drops for the given current.
  4. Jan 1, 2014 #3
    My physics teacher was able to help me. I was missing the fact that the current would have to be made negative since the charger was inputting a current. Thanks though!!
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