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Homework Help: Induced EMF

  1. May 8, 2010 #1
    1. The problem statement, all variables and given/known data
    A flat coil of wire consisting of 20 turns, each with an area of 50 cm^2 is positioned so that the normal to its plane is at the angle of 30 degrees to a uniform magnetic field that increases its magnitude at a constant rate from 2.0T to 8.0T in 2.0 s.

    2. Relevant equations
    Induced EMF(E)= -rate of change of magnetic flux/ change of time

    3. The attempt at a solution
    Induced EMF(E)= rate of change of magnetic flux/ change of time
    or = (N)(Change of B)(A)(COS Theta)/ Change of Time

    A= 50 cm^2
    Change of Time= 2.0 S
    COS 30 degrees= .87
    Change of B= 8.0T-2.0T=6.0T

    The solution as posted by the teacher was,

    Induced EMF(E)= (20)(6.0T)(.005M^2)(.87)/ 2 s
    = .260 V

    I do not understand how 50 cm^2 becomes .005M^2
    also what happened to the negative sign?

    Thank you!
    Last edited: May 8, 2010
  2. jcsd
  3. May 8, 2010 #2
  4. May 8, 2010 #3
    The negative sign is only introduced to show that the emf is in the opposite direction of the change in flux producing it (check out Lenz's Law).

    Now, to convert [tex] 50 cm^2 [/tex] you could go about it this way:

    [tex] 1cm^2 = 0.0001m^2 [/tex]
    [tex] 50cm^2 = x m^2 [/tex]

    [tex] x = 50 \times 0.0001 / 1 = 0.005m^2 [/tex]
  5. May 8, 2010 #4
    Thank you!
  6. May 8, 2010 #5
    No problem. Make sure you're familiar with unit conversions, you'll tend to encounter these a lot as you go along.
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