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

Question

A) A capacitor consists of two closely spaced metal conductors of large area, separated by a thin insulating foil. It has an electrical capacity of 3600.0 F and is charged to a potential difference of 69.0 V. Calculate the amount of energy stored in the capacitor.

B) Calculate the charge on this capacitor when the electrical energy stored in the capacitor is 6.48 J.

C) If the two plates of the capacitor have their separation increased by a factor of 5 while the charge on the plates remains constant, by what factor is the energy stored in the capacitor increased?

Explanation / Answer

A)

C = Capacitance = 3600 u F = 3600 x 10-6 F

V = 69 volts

E = energy stored

Energy stored is given as

E = (0.5) CV2 = (0.5) (3600 x 10-6 ) (69)2 = 8.57 J

B)

E' = energy stored = 6.48 J

V' = Potential difference

Using the formula

E' = (0.5) CV'2

6.48 = (0.5) (3600 x 10-6 ) V'2

V' = 60 volts

Charge stored is given as

Q' = CV' = (3600 x 10-6 ) 60 = 0.216 C

C)

Energy stored is also given as

E = Q2/2C

Q is unchanged . but when seperation is increased by 5 , the Capacitance decrease and becomes 1/5 times

so energy becomes 5 times

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