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Homework Help: Electric fields at points?

  1. Jan 20, 2007 #1
    Hi,

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

    You've hung two very large sheets of plastic facing each other with distance d between them, as shown in Figure P26.50 ( http://i137.photobucket.com/albums/q208/infinitbelt/p26-50-1.gif [Broken]... ). By rubbing them with wool and silk, you've managed to give one sheet a uniform surface charge density n1 = -4(n0) and the other a uniform surface charge density n2 = 5(n0). What is the electric field vector at points 1, 2, and 3?


    2. The attempt at a solution

    I drew the force diagrams for the three points but that is where I think I am making my mistake. For example, for point 1, I have a force going to the left from the positive plate and a force going to the right from the negative plate. The difference I get is 1(n0), but that is wrong. Any ideas?


    Thanks!
     
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Jan 21, 2007 #2
    Any ideas?

    Thanks!
     
  4. Jan 21, 2007 #3

    marcusl

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    Use the expression (probably in your book?) for the electric field from a uniformly charged sheet. The field at each point is a superposition (sum) of the fields from the two sheets.

    For my own clarification; is "n0" a given surface charge density?
     
  5. Jan 21, 2007 #4

    There is no numerical value given to "n0" in the problem. It is like -4x and 5x.

    Thank you for the help!
     
  6. Jan 22, 2007 #5

    marcusl

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    Ok, then the answer will appear as a factor of the electric field from n0.
     
  7. Jan 22, 2007 #6
    What is the expression for the electric field due to the rectangular sheet?

    In my book it is not present. I tried doing the derivation but the integral that I come up with when dividing the sheet into rods doesn't look nice to do. Could you do me the favor and show the expression? Thank you.
     
  8. Jan 22, 2007 #7

    marcusl

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    The field from an infinite sheet with a surface charge density
    sigma is
    [tex]E=\frac{\sigma}{2\epsilon_{0}}[/tex]

    EDIT: fix formula. Note, mks units are used.
     
    Last edited: Jan 22, 2007
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