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Homework Help: Gauss Law Problem to determine F/A

  1. Feb 10, 2010 #1
    Three large but thin charged sheets are parallel to each other as shown in the figure . Sheet I has a total surface charge density of 7.9 nC/m^2, sheet II a charge of -3.3 nC/m^2, and sheet III a charge of 5.4 nC/m^2.

    Figure:

    ----------------(I)
    ----------------(II)


    ----------------(III)

    Estimate the magnitude of the force per unit area on sheet I, II, and III, N/m^2.

    **I do not know how to start**

    Attempt: E=F/Q; Int(E) dA=Q/epsilon




    2. E=F/Q; Int(E) dA=Q/epsilon; [tex]\sigma=Q/A[/tex]



    3. I combined the above eq and got this:
    \sigma*(\sigma)/(2epsilon)
     
  2. jcsd
  3. Feb 12, 2010 #2
    Re: Gauss Law Problem to determine F/A (EDIT)

    The attempt I have done:

    E = σ/2εo

    The force per unit area on sheet I due to sheet II is:

    F = q’E = σ’AE => F/A = σ’E = σ’(σ/2εo) = 3.3x10^-9(7.9x10^-9)/2*8.85x10^-12

    F/A = 1.47x10^-6 N/m²

    or
    FI/A = -σσ’/εo= (3.26x10^-6),

    FII/A = -σσ’/εo + σσ”/εo

    FIII/A = σ’σ”/εo


    ---IT IS NOT RIGHT! HELP ME!!
     
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