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Homework Help: Guass's law nonconducting plates

  1. Feb 11, 2009 #1
    1. The problem statement, all variables and given/known data
    Two very large, nonconducting plastic sheets, each 10.0 cm thick, carry uniform charge densities \sigma_{1}, \sigma_{2}, \sigma_{3}, and \sigma_{4} on their surfaces, as shown in the figure . These surface charge densities have the values sigma_{1}= -6.00microC/m^{2}, \sigma_{2}= +5.00 micro C}/m}^{2}, sigma_{3}= +2.00 micro C}/m}^{2}, and \sigma_{4}= +4.00 micro C}/m}^{2}.

    1.Use Gauss's law to find the magnitude of the electric field at the point A, 5.00 cm from the left face of the left-hand sheet.

    2.Find the direction of the electric field at the point A.

    3.Find the magnitude of the electric field at the point B, 1.25 cm} from the inner surface of the right-hand sheet.

    4.Find the direction of the electric field at the point B.

    5.Find the magnitude of the electric field at the point C, in the middle of the right-hand sheet.

    6.Find the direction of the electric field at the point C.

    2. Relevant equations
    E=(1/4*pi*epsilonnaut)(q/R^2)


    3. The attempt at a solution
    I'm not really sure how to set this problem up. I'm not sure if all the charges act on each point
     

    Attached Files:

  2. jcsd
  3. Feb 11, 2009 #2

    Doc Al

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    Staff: Mentor

    That's the field from a point charge--you won't need that for this problem.

    Use Gauss's law to find the field from a sheet of charge. Then add up all the fields at each point in question.
     
  4. Mar 4, 2009 #3
    I know we have to use E=sigma/2epsilon, but I'm not sure which fields (1 and/or 2 and/or 3 and/or 4) to add together for point A for example.
     
  5. Mar 5, 2009 #4

    Doc Al

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    Staff: Mentor

    They all count--add them all. (Be careful with their direction and sign.)
     
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