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Homework Help: Finding electromotive force

  1. Feb 28, 2013 #1
    1. The problem statement, all variables and given/known data
    A battery has a current of 3.0A flow through it. It has an internal resistance of 0.039Ω and the circuit has a load of 45Ω.
    a) What is the emf?
    b) What is the voltage that flows?

    2. Relevant equations
    V = ε - IR

    3. The attempt at a solution
    ε = V + IR
    ε = (45Ω)(3A) + (3A)(0.039Ω)
    ε = 135V + 0.117V

    a) 135.117V
    b) 135V

    I'm new to emf. Does this look correct? If not, can you explain where I went awry?
  2. jcsd
  3. Feb 28, 2013 #2
    They asked what is the voltage that flows? Are you sure it wasn't current?
  4. Feb 28, 2013 #3
    Not positive, but pretty sure.
  5. Feb 28, 2013 #4
    I would check that. The voltage in a circuit doesn't "flow". The purpose of a battery is to keep the potential difference across two points in a circuit at a specific potential difference.
  6. Feb 28, 2013 #5
    Is part "a" correct? And doesn't current remain constant?
  7. Feb 28, 2013 #6
    Your answer looks good for part a. The current is the same everywhere in a series branch in a circuit. However, current refers to a collection of charges passing through a unit area in time t. Hence, it is often said to "flow".
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