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 3400.0 ?F and is charged to a potential difference of 63.0 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 8.81 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

apply Energy stored in a Capacitor U = 0.5 cv^2

where C is capacitance and V is Volatge

so

U = 0.5 * 3400 e-6 * 63 * 63

U = 6.747 Joules
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again U = 0.5 Q^2/C

so Q^2 = 2UC

Q^2 = 2* 8.81*3400e-6

Q = 0.244 C

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if d is increased by 2, ,  

C = eo A/d, C decreases by 2

V = Ed ,   V increases by 2

so Unew = 0.5 * C/2 * 4v^2

so Unew = 2 times of U

so Unew also doubles = 13.49 Joules

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