9.A capacitor has parallel metal plates separated by an air gap of .250mm. The a

Question

9.A capacitor has parallel metal plates separated by an air gap of .250mm. The arrangement has capacitance of 285pF (1 pf = 10^-12 Farads) and the plates are given opposite charges of +85 nC and - 85nC.
a) Which the given charges on the plates, what is the potential difference between them?

b) How much energy is being stored in the capacitor?

c) If the plates are squares, what size (length of side) are they?

d) The dielectric strength for air is about 3 MV/m. What maximum voltage can this capacitor maintain without sparking occurring between the plates.

Explanation / Answer

1)c= q/v 285*10^-12 = 85*10^-9/v v= 298.2 v 2) energy stored = 0.5 c*v^2 = 0.5*285*10^-12 *(298.2)^2 =12.6*10^-6 watts 3)c= eA/d A= c *d/e = 285*10^-12 *.25*10^-3/8.85*10^-12 =0.08m^2 area of square = side*side lenght of side =squareroot of(area) =8.97*10^-5 m 4)dielectric strength = maximum voltage appled/metre 3*10^6 = max voltage/8.975*10^-6 max voltage = 26.9 volts

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