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Homework Help: Emf and coils

  1. Feb 19, 2008 #1
    1. The problem statement, all variables and given/known data

    In each of two coils the rate of change of the magnetic flux in a single loop is the same. The emf induced in coil 1, which has 200 loops, is 2.67 V. The emf induced in coil 2 is 3.78 V. How many loops does coil 2 have?

    2. Relevant equations

    E=-N(delta Phi/delta t)

    3. The attempt at a solution

    i tried setting E+N=E+N because the magnetic flux is the same but that was wrong
     
  2. jcsd
  3. Feb 19, 2008 #2
    F=d(phi)/dt for ease of writing and I always use V if I'm not using the little epsilon for emf

    So you got V1+N1*F=V2+N2*F

    you can't just get rid of F like you did. Note that you're actually given enough information to SOLVE for F directly just using the equation you were given, then use it to find N
     
  4. Feb 19, 2008 #3
    i'm confused what equation do i use to find F? i have no time so how can I use that equation?
     
  5. Feb 19, 2008 #4
    The equation that you just typed in the relevant equations section. For coil 1 you're given N and E, so certainly you can find the change in flux, then just use that same number for coil 2's E to find N
     
  6. Feb 19, 2008 #5
    i got 202.67 for the change in flux of the first coil and .01865 for N of the second coil. that doesn't seem like it is right. is it?
     
  7. Feb 19, 2008 #6
    Nope, for coil 1, you have this equation

    E=-N(delta Phi/delta t)

    You're given E=2.67, and N=200, so you can solve for dphi/dt, which is gonna be 2.67/200, and a pretty small number
     
  8. Feb 19, 2008 #7
    ok then 283.15 turns?
     
    Last edited: Feb 19, 2008
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