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Capacitor. Find thickness of polystyrene

  1. Apr 7, 2014 #1
    1. The problem statement, all variables and given/known data

    A 490 pF capacitor consists of two 19 cm -radius circular plates, insulated with polystyrene

    Find the thickness of the polystyrene.

    2. Relevant equations

    d = (ε_0 * Area * K) / C

    3. The attempt at a solution

    I converted 490 pF to F

    4.90 * 10^-10 F

    I converted 19 cm to meters

    .19 m

    and found the area of the plate

    ∏r^2 = ∏(.19)^2 = .1134 m^2

    K of polystyrene = 2.3, so now just plug everything into my equation

    d = ((2.3) * (8.854*10^-12) * (.1134)) / (4.9 * 10^-10)

    d = .00471 m

    I want my answer in mm with two significant figures

    d = 4.7 mm

    mastering physics tells me this is the wrong answer, where did I go wrong?
  2. jcsd
  3. Apr 7, 2014 #2
    never mind, I found it. the value for K was 2.6 not 2.3, I was mistaken
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