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Homework Help: Electromotive force

  1. Apr 8, 2010 #1
    1. The problem statement, all variables and given/known data
    So i'm trying to figure out what exactly is emf in a ciruit and this is what i understand so far:
    A source of emf converts some form of energy into electrostatic potential energy needed in order to do work to separate positive and negative charges at its terminal against the repulsion of charges already there.' Does this sound right?
    But then it says in my book that a 'emf is defined as the work per unit charge by the source of emf in moving the charge around a closed loop..' i'm confused by this..Do they basically mean that it does work to separate negative and positive charges at their terminals by moving negative charges from one of the terminals (which gives it an excess positive charge at this terminal) around the loop and into the other terminal (which gives it an excess negative charge)?



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Apr 9, 2010 #2
    EMF is the same thing as voltage. In SI units, one volt is given as one newton meter per coulomb, thus emf is the energy per unit charge. The work-energy theorem leads to the definition of emf as the amount of work done by the source on the charge in moving it around the circuit.

    By convention, we consider electric current to be positive charges moving through the circuit from the positive terminal to the negative terminal. This means that we are considering the electric field set up by the emf source to be doing work on the charge which, in turn, delivers energy to the circuit.
     
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