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Homework Help: Flux - simple integral computation

  1. Oct 6, 2009 #1
    1. The problem statement, all variables and given/known data
    A surface has the area vector A = 2i + 3j. What is the flux of a uniform electric field through it if the field is E = 4i?

    2. Relevant equations
    Integral calculus, vectors

    3. The attempt at a solution
    I don't understand why one could do this. The integral is of E and dA, not E and A. How can I use A to determine dA?

    This is a crackpot way I thought of

    [tex] \Phi = \int \vec{E} \cdot \vec{dA} [/tex]

    [tex]
    \Phi = \vec{E} \cdot \int \vec{dA}
    [/tex]

    [tex]
    \Phi = \vec{E} \cdot \vec{A}
    [/tex]

    Then Phi = 4i dot (2i + 3j) = 8 flux units

    This seems like wild fantasy though as I don't know if I can pull out a constant from a dot product integral
     
  2. jcsd
  3. Oct 6, 2009 #2

    kuruman

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    There is no dA to speak of. You are given A which is the same everywhere and E which is uniform. Just take the dot product as you have in your third equation. There isn't much to this problem/
     
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