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Homework Help: Increasing EMF in a coil

  1. Oct 3, 2009 #1
    1. The problem statement, all variables and given/known data

    This is the solution to one of the problems I came across:
    In an AC generator, a coil spins in a magnetic field. Of the following choices, circle the
    one that will not cause an increase in the EMF generated in the coil?
    a. replacing the coil wire with one of lower resistance.
    b. spinning the coil faster.
    c. increasing the magnetic field.
    d. increasing the number of turns of wire on the coil.
    e. all of the above actions will increase the EMF.

    Explain your choice.
    A is the correct answer
    • Lower resistance wire will not affect the EMF, which is
    proportional to the rate of change of flux.
    • It would however, increase the current possible.

    I would like to know if EMF is the same as V = IR (Ohm's law)? Hence if resistance decreases, then EMF would decreased since V is proportional to R. Why then do the answers to this question say that resistance will not affect the induced EMF?

    2. Relevant equations
    EMF = (change of flux)/ time
    V = IR

    3. The attempt at a solution
    Please see above, part 1.
  2. jcsd
  3. Oct 3, 2009 #2


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    Science Advisor
    Homework Helper
    Gold Member

    Yes, it is like V = IR but you are confused about how to apply it. You can think of the induced emf as a battery the "voltage" of which depends on things like the frequency of rotation, magnetic field. etc. - there is a formula for this. Now if you take a 6 Volt battery and you hook it up to a wire, you will get a current. If now you hook up a wire of lower resistance, will the battery stop being a 6 Volt battery? No, it will just put out more current so that the product IR is constant. Same situation here.
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