Physics help Please!!!! Energy Released from capacitor?

Question

Consider the parallel-plate capacitor formed by the Earth and a cloud layer. (The cloud layer is 1000 m above the Earth and has an area of 0.7 km2 = 0.7 106 m2.) Assume this capacitor will discharge (i.e., produce lightning) when the electric field strength between the plates reaches 3.1 106 N/C. What is the energy released if the capacitor discharges completely during a lightning strike?

Answer 1

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E = 3.1x 10^6 N/C

A =0.7 x10^6 m2

d=1000 m

e=permittivity of air = 8.85x10^-12F/m

The energy stored on a capacitor is in the form of energy density in an electric field is given by

n =( energy/volume) = (1/2)eE^2

Energy = nV = (1/2)eE^2(V) = (1/2)eE^2(A/d)

Energy released = (1/2)(8.85x10^-12)(3.1x 10^6)^2(0.7 x10^6/10^3)