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Homework Help: Average induced emf in coil with turns

  1. Feb 25, 2012 #1
    1. The problem statement, all variables and given/known data
    A closely wound rectangular coil of 95.0 turns has dimensions of 29.0 cm by 40.0 cm. The plane of the coil is rotated from a position where it makes an angle of 39.0 degrees with a magnetic field of 1.60 T to a position perpendicular to the field. The rotation takes 0.120 s.
    What is the average emf induced in the coil?


    2. Relevant equations



    3. The attempt at a solution
    ε=ΔB/Δt*(A*cos 39°)
    ε=1.6/.120*(.116*cos39)
    =1.20
    This is the wrong answer!
     
  2. jcsd
  3. Feb 26, 2012 #2

    I like Serena

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    Homework Helper

    Welcome to PF, susan14! :smile:


    Which formula do you have for the emf?

    I have:
    $$\mathcal{E}=-N {d\Phi \over dt}$$
    where either ##\Phi = B_{\textit{perpendicular to A}} A## or ##\Phi = B A_{\textit{perpendicular to B}}##.




    The average ##\mathcal{E}## would be:
    $$\mathcal{E}_{average}=-N {\Delta\Phi \over \Delta t}=-N {\Phi_t - \Phi_0 \over t - 0}$$
    where ##\Phi_0## is the magnetic flux at time t=0, and ##\Phi_t## is the magnetic flux at the final time t.

    What would you get for ##\Phi_0## and for ##\Phi_t##?
    And what did you do with the factor N?
     
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