A capacitor consists of two closely spaced metal conductors of large area, separ

Question

A capacitor consists of two closely spaced metal conductors of large area, separated by a thin insulating foil. It has an electrical capacity of 4000.0 mu F and is charged to a potential difference of 72.0 V. Calculate the amount of energy stored in the capacitor. Calculate the charge on this capacitor when the electrical energy stored in the capacitor is 7.20 J. If the two plates of the capacitor have their separation increased by a factor of 2 while the charge on the plates remains constant, by what factor is the energy stored in the capacitor increased?

Explanation / Answer

a)

here the formula of energy stored is

U = 0.5 *C * V^2

U = 0.5 * 4000 * 10^-6 * 72^2

U = 10.368 J

b)

here also we use the same formula

U = 0.5 *Q *V

7.2 = 0.5 * Q * 72

Q = 0.2 C

c)

U = 0.5 * Q^2 / C

distance is increased

U = 0.5 * Q^2 / (C/2)

U = Q^2 / C

so the enrgy stored is increased by factor 2

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