Polystyrene has dielectric constant 2.6 and dielectric strength 2.0 times 10^7 V

Question

Polystyrene has dielectric constant 2.6 and dielectric strength 2.0 times 10^7 V/m. A piece of polystyrene is used as a dielectric in a capacitor, sing the volume between the plates When the electric shield between the plates is 82% the dielectric strength, what is the energy density of the stored energy Express your answer with the appropriate units. when the capacitor is connected to a battery with voltage 500.0 V, the electric field between the plates 82 % of the dielectric strength what is the area of each plate if capacitor stores 0.25 mJ of energy under these conditions? Express your answer with the appropriate units.

Explanation / Answer

energy density = energy/volume

n = 1/2*C*V^2/A*d

using

C =k*eo*A/d

V = E*d

U = 1/2 * k *eo*E^2

here E = 2 x 10^7 * 0.82

k = 2.6

eo = 8.85 x 10^-12

U = 3094.38 J

part b )

U = 1/2 * CV^2

U = 0.25 mJ = 0.25 x 10^-3 J

V = 500 V

C = 2 x 10^-9 F

we know C = k*eo*A/d

here we know V = E*d

d = V/E

d = 3.045 x 10^-5 m

A = 2.65 x 10^-3 m = 26.5 cm

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