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Homework Help: Please help! Electric field!

  1. Oct 28, 2004 #1
    Two thin long charged metal plates are placed at x = 0, and x = d (that means they are plaed vertically, parallel to the Y Axis. Thus the distance between them is d. Assume that V(x=0) = 0, and that the thickness of the plates is lesser than d.

    a) Find E(x) and V(x) when 0 < x < d.

    First of all let the surface charge density [tex] \sigma = \frac{Q}{A} [/tex]

    If i use Gauss Law then the Electric field [tex] E = \frac{\sigma}{\epsilon_{0}} [/tex] since the plates are conducting surfaces.
    To find [tex] V(x) = \int E \cdot dx = \frac{\sigma}{\epsilon_{0}} \cdot dx = \frac{\sigma}{\epsilon_{0}} x [/tex]

    i'm not really sure if i derived that expression correctly for V(x) which i why i need your help, please.

    b) Find E(x) and V(x) if x > d
    E(x>d) = zero or kq / (x+d)^2
    V(x>d) = zero as well? or simply integrate E over x??

    c) Find E(x) and V(x) if x<d
    same as the previous one?? i.e. both E and V are zero?? Not realy sure here either?

    d) Sketch E(x) and V(X)
    I m not really sure about my expressions in a so if i found those out properly, with your help i can easily do this one!

    Thank you in advance for your help!!

    Attached Files:

    Last edited: Oct 28, 2004
  2. jcsd
  3. Oct 29, 2004 #2
    so is ther anyone out there who can help me!!!

    i am cofnused about hte first part whether E = kq/r^2 or E = constnat

    but then the graphing part would be useless no?

    And wha about the outsides of the plates?
  4. Oct 29, 2004 #3


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    Homework Helper

    Your E field and potential for the middle region (0 < x < d) are correct!

    For x > d the electric field will be zero (it's discontinous due to the charge) and likewise for x < 0. However, the potential will be continuous across those surface.
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