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Homework Help: Magnetic Field from a Graph?

  1. Mar 9, 2007 #1
    1. The problem statement, all variables and given/known data
    I have a graph of an emf of a generator vs time, and i know the cross-sectional area per turn is 0.03m^2 and there are 160 turns. From the wave graph I figured out the frequency of the generator is 2.4Hz and the angular speed is 14.96rad/s. I need to figure out the magnetic field.


    2. Relevant equations
    e=-NAcos0B/t


    3. The attempt at a solution

    I found the frequency and angular speed from the graph but I have no idea how to find the magnetic field from a graph. Please help. Thank you.
     
  2. jcsd
  3. Mar 10, 2007 #2
    It's important to realise that the emf is directly proportional to the change of magnetic flux:

    [tex]\Phi = BS\cos{\omega}t[/tex]

    [tex] emf = -N \frac{d\Phi}{dt}[/tex],

    that is:

    [tex] emf = -NBS \frac{d}{dt}\cos{\omega}t = -NBS\omega\sin{\omega}t[/tex]

    Then rearrange it to get the formula for B.
     
    Last edited: Mar 10, 2007
  4. Mar 10, 2007 #3
    Ok so I rearranged the formula to get B=emf/-NAwsinwt
    = 28/(-160)(.03)(14.96)(sin(14.96*.315))
    =28/71.808
    =0.38993
    Is that correct? Thanks!
     
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