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Electric circuit problem, finding internal resistance

  1. May 19, 2013 #1
    1. A battery whose emf is 6.0 V is connected to a 2.0 Ω resistor. The voltage drop across the 2.0 Ω resistor is 5.0 V. What is its internal resistance?

    a) 0.40 Ω
    b) 1.7 Ω
    c) 2.4 Ω
    d) 2.5 Ω

    2. Relevant equations


    3. The attempt at a solution

    I know that

    ε=6.0 V
    VT=5.0 V
    and a resistor= 2.0 Ω

    The resistor part is what I don't understand. If I'm looking for the internal resistance, I'm looking for the resistance of the resistor. So if they give me the resistance to be 2.0 Ω in the question, shouldn't the answer be 2.0?

    The answer is a) 0.40 Ω.
  2. jcsd
  3. May 19, 2013 #2


    User Avatar

    Staff: Mentor

    You're looking for the internal resistance of the battery.
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