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Homework Help: Internal Resistance

  1. Feb 25, 2008 #1
    1. The problem statement, all variables and given/known data

    "A 6.0V battery is connected across a parallel combination of two resistors ; one 10 ohm and one 40 ohm. Thee total current provided by the battery is 0.25A. Obtain a value for the internal resistance.

    2. Relevant equations

    E= IR +Ir

    3. The attempt at a solution

    I find the combined resistance of the resistors to be 8 ohms, and sub this in to the equation above, and solve for little r, but get an answer of 16 ohms; the correct answer, according to the answer book is 4 ohms. Please can you show me a correct solution to the question!

  2. jcsd
  3. Feb 25, 2008 #2
    Your answer is correct. Since 6.0 V produces 0.25 A of current, R+r must be 24 ohms.
    10 and 40 ohms parallel is indeed 8 ohms, so r must be 16 ohms.
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