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What is the electric flux through the top surface of the cube?

  1. Jan 22, 2008 #1
    1. The problem statement, all variables and given/known data

    A 3 nC point charge is at the center of 5 m x 5 m x 5 m cube. What is the electric flux through the top surface of the cube?

    2. Relevant equations

    E=kq/r^2
    φ = E.A

    3. The attempt at a solution

    E = (8.99*109)(3*10-9) / 2.52 = 4.3152 N/C

    φ = E.A = (4.3152)(5*5) = 107.88
    But, it is wrong. Can someone please tell me what I am doing wrong?
     
  2. jcsd
  3. Jan 22, 2008 #2
    You assume a constant electric field over the whole top surface

    The equation E=kq/r^2 where r is, I assume you put in 5, only the electric field at the center of the top. Every other point on the top is gonna have a different r and electric field, it's not constant.

    Edit: actually for r it looks like you used...sqrt(2.52)? I'm not sure where that came from
     
    Last edited: Jan 22, 2008
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