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Homework Help: Flux through a loop of wire in a magnetic field.

  1. Mar 5, 2009 #1
    1. The problem statement, all variables and given/known data
    A uniform 4.5 T magnetic field passes perpendicularly through the plane of a wire loop .10 m^2 in area. What flux passes through the loop?

    2. Relevant equations
    Flux = (B)(A)[cos(theta)]

    3. The attempt at a solution

    Ok, according to my understanding. The equation should be set up as such:

    flux = (4.5)(.10)[Cos(90)]

    The cosine of 90 degrees, obviously, is zero therefore there should be no flux through the wire loop, correct? The answer sheet to this review is saying that the answer to this problem is

    (b) .45 Tm^2

    This would be true if the equation was the "sine of theta" rather than the cosine of theta, right? Is my equation wrong or is the review sheet wrong?!


  2. jcsd
  3. Mar 5, 2009 #2


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    Staff Emeritus
    Science Advisor

    The normal to the plane of the loop is parallel to the B-field.

    With respect to area, the area vector is perpendicular (normal) to the area surface by convention.
  4. Mar 5, 2009 #3
    And perpendicular = 90 degrees, so my equation should reduce to zero because the cosine of 90 degrees is zero?

    Or am I missing the point of your post? lol
  5. Mar 5, 2009 #4
    Oh i get it! Haha, duh.

    The normal is perpendicular to the surface making the angle 0 degrees. Cosine of 0 is 1. Yeah, I'm running on very little sleep, lol.

    thanks, Astronuc.
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