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Homework Help: Electric field: please help

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

    The conducting box has been given an excess negative charge. The surface density of excess electrons at the center of the top surface is 31 x 10^10 electrons/m^2. What is the electric field strength at point 1?
    http://img401.imageshack.us/img401/680/knightfigure27262bn2.jpg [Broken]
    2. Relevant equations

    E = linear charge density/E0
    linear charge density=q/L

    3. The attempt at a solution
    First I found the charge
    =(31*10^10 electrons/m^2)*(1.6*10^-19)
    =5*10^-8 C/m^2
    E=(5*10^-8 electrons/m^2)/(8.85*10^-12)
    Can someone please conform if am right ?

    Attached Files:

    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Jan 22, 2008 #2
    please upload your images at a service like http://imageshack.us or http://bayimg.com [Broken] . We are not able to see your attachment as it is pending approval...
    Last edited by a moderator: May 3, 2017
  4. Sep 13, 2010 #3
    This is correct. We can double check by looking at the units. Finding the charge gives us:

    q=Ne=(31*10^10 electrons/m^2)*(1.6*10^-19 C/electron)
    =5*10^-8 C/m^2

    Than dividing by the permittivity constant, 8.85*10^-12 C^2/Nm^s gets the units into the units of electric field, N/C
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