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Homework Help: Electric Flux with angles

  1. Jul 17, 2007 #1


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    1. The problem statement, all variables and given/known data

    The drawing shows an edge-on view of two planar surfaces that intersect and are mutually perpendicular. Surface 1 has an area of 1.2 m², while surface 2 has an area of 3.5 m². The electric field E in the drawing is uniform and has a magnitude of 246 N/C.


    http://img513.imageshack.us/img513/9947/physicspf4.jpg [Broken]

    What's the electric flux through surface 1? What about surface 2?

    2. Relevant equations

    [tex]\Phi = EAcos\Theta[/tex]

    3. The attempt at a solution

    For #1, I attempted to do 246*1.2*cos(55°), which is incorrect at 169.3197 Nm²/C.

    What exactly am I screwing up here?
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Jul 17, 2007 #2


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    If the field is perpendicular to the surface then flux is just EA. From this we conclude that the angle in your formula is the angle that the field makes with a normal to the surface, not the angle it makes with the surface.
  4. Jul 17, 2007 #3


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    Yeah, I was thinking things through and got my angles a bit mixed in the process, as you can see.

    Got it now - thanks.
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