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Force between to charged plates

  1. Nov 10, 2008 #1
    1. The problem statement, all variables and given/known data
    Two thin flat plates measure 1m by 1m and are separated by 0.005m. They are oppositely charged with one plate being +15*10^-6 C and the other -15*10^-6 C.
    Estimate the total forces exerted by one plate on the other


    2. Relevant equations

    F=kq1q2/r^2
    [tex]
    \int {\vec E \bullet d\vec A} = \frac{{Q_{enc} }}{{\varepsilon _0 }}
    [/tex]

    [tex]
    F = qE
    [/tex]

    3. The attempt at a solution

    I realised that I attempted this as point charges by the distance between is relatively small in comparison with area
    When I did this i calculated it to be 80926 N which is wrong, answer is given as 13N

    Than I approached from Guass's law

    [tex]
    \begin{array}{l}
    \int {\vec E \bullet d\vec A} = \frac{{Q_{enc} }}{{\varepsilon _0 }} \\
    EA = \frac{{Q_{enc} }}{{\varepsilon _0 }} \\
    A = 1m^2 \\
    E = \frac{{Q_{enc} }}{{\varepsilon _0 A}} \\
    \end{array}
    [/tex]

    so electric field from one plate is equal to
    [tex]
    E = \frac{{15 \times 10^{ - 6} }}{{(8.85 \times 10^{ - 12} ) \times 1}} = 1.695 \times 10^6 N/C
    [/tex]

    and so the force from one plate is
    [tex]
    \begin{array}{l}
    F = qE \\
    F = (15 \times 10^{ - 6} )(1.695 \times 10^6 )=25.43N \\
    \end{array}
    [/tex]

    Anyone able to help me here with this. Thanks
     
    Last edited: Nov 10, 2008
  2. jcsd
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