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Homework Help: What is the value of the loss volt and internal resistance of the battery?

  1. May 9, 2008 #1
    1. The problem statement, all variables and given/known data
    When a current of [tex]2A[/tex] flows the p.d across a battery's terminal falls from [tex]12V[/tex] to [tex]9V[/tex].
    (a) What is the value of the loss volt?
    (b) What is the internal resistance of the battery?

    2. Relevant equations
    Lost Volt = Ir

    3. The attempt at a solution
    (a) [tex]12V - 9V = 3V[/tex]

    [tex]R = \frac{V}{I} = \frac{3}{2} = 1.5[/tex]

    [tex]Lost Volt = 3 \times 1.5 = 4.5[/tex]

    Is this correct?

    (b) Don't know which equation to use :confused:
  2. jcsd
  3. May 10, 2008 #2
    your last 4.5 is wrong and no need. It is (lost volt)*(internal rezistance of battery) and meaningless.

    Lost volt: 3V
    R=1.5 ohm
  4. May 10, 2008 #3


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    Staff Emeritus
    Science Advisor
    Homework Helper

    You can always check by using units in the calculation:
    [tex]3V \times 1.5 \mbox{ohms} = 4.5 \ V\times \mbox{ohms} [/tex]

    Since the units (V x ohms) are not Volts, this can't be right.

    R = V/I, you already did it without realizing it :smile:
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