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How does emf relate to current, elec potential, & resistance

  1. Mar 3, 2016 #1
    1. The problem statement, all variables and given/known data

    How does emf relate to current, electrical potential, and resistance? Specifically, in the context of the equations I have posted below.

    2. Relevant equations

    V = IR
    where V is electric potential, I is current, and R is resistance.

    V = emf - IR

    How can V = emf - IR if V = IR ?
    Here is another similar example:

    R = V/I

    R = (emf - V) / I


    3. The attempt at a solution

    emf seems to be some kind of change to the original electric potential of a circuit. emf - IR seems to calculate ΔV. Am I right about this? As far as I can tell, Ohm's law uses V, not ΔV. When is ΔV useful and when is V useful? Or do I have this all wrong?


    Thanks.
     
  2. jcsd
  3. Mar 3, 2016 #2

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    I think some context is missing.

    Can you draw the circuit for the examples you mention. Are you talking about a battery with internal resistance or a DC motor or ????
     
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