Capacitor. Find thickness of polystyrene

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?

http://ift.tt/1kimf15

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