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Homework Help: Leakage Resistance

  1. Jan 19, 2010 #1
    1. The problem statement, all variables and given/known data
    A non ideal capacitor having a 'leaky' dielectric where RL is the leakage resistance measured across the dielectric. A 100pF parallel plate capacitor has a mica dielectric of relative permittivelty Er = 12 and resistivity of p = 1014 ohm m.
    Calculate the leakage resistance of this capacitor





    2. C = Er A/d & R = p d/A



    3. Ans
    C = 100 pF, resistivity = 1014 ohm m
    Er = 12
    C = Er A/d ---- (1)
    where A is the area of cross section of the plate and d is the distance between the plates ( or the length of the dielectric)
    R = p d/A ----(2)
    From (1), d/A = Er/C = 12/(100 x 10-12) = 12 x 1010
    Substituting in (2)
    R = 1014 x 12 x 1010
    Or R = 12 x 1024 Ohm
    Or R = 1.2 x 1025 Ohm

    The Equation seems right however answer looks wrong
     
  2. jcsd
  3. Jan 19, 2010 #2
    You have the right idea. However, in the formula for the capacitance you are missing the vacuum permittivity E_0 = 8.85419 * 10^-12 F/m

    C = E_0 E_r A/d

    Always check your units!
     
  4. Jan 20, 2010 #3
    Roger, of course - thanks for pointing that out, appreciated
     
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