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Homework Help: Electric Flux through an Infinite Plane due to a Point charge

  1. Jun 8, 2007 #1
    1. The problem statement, all variables and given/known data

    A point charge of 43 microcoulombs is located a distance 48 meters from an infinite plane. Determine the electric flux through the plane due to the point charge.

    2. Relevant equations

    flux = integral E d A = enclosed charge / epsilon_0
    E = kQ / r^2

    3. The attempt at a solution

    Well first off. This is the first problem of the assignment. I've finished EVERY other problem including the ones that require me to actually work out line integrals. No problem. But this one is stumping me.

    I know how to calculate say.. the electric flux through some area of the plane.. using flux = EA.. and if I had the surface charge density I could easily just use a cylinder (gaussian surface) to find the answer. But with an infinite plane.. with no mention of any of its properties.. I seem to have reached the limit of my understanding of flux.

    I tried the obvious 43 microcoulombs / episolon_0 and that submitted as incorrect.

    So I'm stumped and have no clue how to proceed.

    Would I want to calculate the E? A distance is given. so I can find out kQ/(43m)^2 but then I need an area to multiply that by.. and infinity doesn't really lend itself well to multiplication. (at least not in the case where you're trying to submit the answer online)
  2. jcsd
  3. Jun 8, 2007 #2

    Doc Al

    User Avatar

    Staff: Mentor

    If you want, you can find the field at any point on the plane and integrate to find the flux. But there's a much simpler way. Imagine the field emanating in all directions from the point charge. How much of it passes through the infinite plane? What fraction of the total flux?
  4. Jun 8, 2007 #3

    Submitted and correct. Thank you.

    I had a feeling it would be something embarassing :p
    Last edited: Jun 8, 2007
  5. Jun 13, 2007 #4
    I have a feeling that you're in my class.

    anyway, thanks for the tip, doc al...
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