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Faraday's law problem

  1. May 3, 2007 #1
    1. The problem statement, all variables and given/known data

    Take a loop of wire with a radius of 2.0 cm. A B field is perpendicular to the area enclosed by the wire. If the field is reduced to zero from 0.55 T in 0.25 s, what is the induced emf between the ends of the wire?



    2. Relevant equations
    B=Magnetic Field
    A=Area
    Flux= BA cos(Theta)
    EMF = Change in Flux/ Change in time

    3. The attempt at a solution

    Trying to find Flux but since its perpendicular to the area, cos90 = 0 and this makes no sense. The answer is suppose to be 0.0028V. Any help would be great, Thanks
     
  2. jcsd
  3. May 3, 2007 #2
    Your geometry is wrong. You're using the wrong angle.
     
  4. May 3, 2007 #3
    ok my bad its suppose to be cos0 which is 1
    with that i found Flux to be = (0.55T)(4pi) which is around 6.9T/m^2
    With that 6.9(T/m^2)/0.25(Secs)= 27.6 Volts?
    Like i said answer is suppose to be 0.0027V. Is there something wrong or did i just screw up the units some where?
    Thanks again...
     
  5. May 3, 2007 #4
    Again the issue is geometry. Look carefully as how you're calculating the area.
     
  6. May 3, 2007 #5
    The area is just( pi)r^2 right?
     
  7. May 3, 2007 #6
    Yes, but be careful what you use for "r".
     
  8. May 3, 2007 #7
    Ohh. I see. its in cm. that should change things abit...Thanks everyone.
     
  9. May 3, 2007 #8
    Success! I have to ask this question: What about physics did you learn from doing this problem?
     
  10. May 3, 2007 #9
    ... wat did i learn? I hate physics Tests. =D and UNITS.
     
  11. May 3, 2007 #10
    Your answer is more or less correct. My point is that there wasn't much physics in this problem.
     
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