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Average emf

  1. Apr 3, 2009 #1
    1. The problem statement, all variables and given/known data
    1. When a 100 loop coil of wire of radius 2.00 cm is rotated in a uniform magnetic field,B=0.500T , so that it goes from maximum flux to zero flux in 0.0320 s, find the average emf induced between the terminals of the coil.


    2. Relevant equations

    Max Flux=BAcos(0)=Change in flux

    E=-N change in flux/change in time


    3. The attempt at a solution

    E=[-N(BAcos0)]/t

    E=[-100(0.500T pi(2.00cm2) cos 0o)]/0.0320s

    How do I calculate average emf? should I just divide by 0.0320s again?
     
  2. jcsd
  3. Apr 3, 2009 #2

    Redbelly98

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    Dividing by 0.0320 s just one time, as you have already done, will give average EMF.

    Avg EMF = N Δ(Flux) / Δt​
     
  4. Apr 4, 2009 #3
    Thank you.
    Is it possible to calculate instantaneous emf? and would there ever be a use for such a calculation?
     
    Last edited: Apr 4, 2009
  5. Apr 4, 2009 #4

    Redbelly98

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    Yes and yes.

    Have you had calculus? Instantaneous emf is the derivitive (w.r.t. time) of N x flux, where
    flux = B A cos(ωt)​

    It's useful for power generators, which operate on the principle of induced emf.
     
  6. Apr 6, 2009 #5
    No I have not had any calculus. I am taking physics 12 right now. I am going to university next year to start an engineering degree so I will be into it soon enough.
     
  7. Apr 6, 2009 #6

    Redbelly98

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    Okay.

    Instantaneous EMF can be approximated by
    EMF = N Δ(Flux) / Δt
    as long as Δt is a small amount of time, a lot smaller than one oscillation period.

    The smaller Δt is, the better the approximation.

    In the above homework, Δt corresponded to 1/4 of a period (the time to go from maximum to zero). It would have to be a lot smaller than that in order to get a decent approximation.
     
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