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Charge in a cube

  1. Sep 19, 2006 #1
    There is a positive charge located at the center of a cube.

    are the intersections of the field lines with a side of the box uniformly distributed across that side? (can someone also give a clear definition of what uniformly distributed means?)

    describe how the field lines for the positive point charge appear to be distributed when the region over which you look becomes sufficiently small.

    thank you for any input. ive been up for hours on this wonderful crap :)
  2. jcsd
  3. Sep 19, 2006 #2


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    Uniformly distributed would mean no spatial depdence on the flux, i.e. the field line density would be independent of position on the face.

    Assume the positive charge is a point charge. What is the dependence on the field strength (field line density) as function of distance from the point source? What can one say about the loci of points on the face of a cube in relationship to the center of the cube?

    What happens as the dimensions of the cube shrink to the point charge?
  4. Sep 19, 2006 #3
    so the center of the cube should have a stronger electric field. the electric field should not be uniformly distributed.

    and if the dimensions of the cube shrink, then the field lines would look like they're denser.....

    i think... im not sure. am i closer to the truth? ^^
  5. Sep 19, 2006 #4


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    You are getting close.

    If the E field lines have a dependence on r (radial distance from charge), what can be said about the uniformity on a flat surface?

    What happens to the square surface (cube face) as r gets smaller, i.e. r -> 0? What happens to the uniformity or non-uniformity as a result?
  6. Sep 19, 2006 #5
    to answer the first question, there is no uniformity on a flat surface because the field lines hit the surface at different distances. im pretty sure of this.

    if the r gets smaller, then the electric field should increase, and it should become more uniform....
  7. Sep 19, 2006 #6


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    Right on! :cool:
  8. Sep 19, 2006 #7
    thanks very much! :)
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