A parallel-plate capacitor has plates with an area of 420 cm2 and an air-filled

Question

A parallel-plate capacitor has plates with an area of 420 cm2 and an air-filled gap between the plates that is 2.50 mm thick. The capacitor is charged by a battery to 550 V and then is disconnected from he battery. Part A How much energy is stored in the capacitor? U. 22.5 ? Previous Answers Correct Part B The separation between the plates is now increased to 4.20 mm. How much energy is stored in the capacihor now? Submit Previous Answers Reauest Answer Incorrect; Try Again; 7 attempts remaining 15

Explanation / Answer

a) A = 420 cm2 = 420 * 10-4 m2

C = e0 A / d = (8.85 * 10-12 * 420 * 10-4 ) / (2.5 * 10-3) = 1.49 * 10-10 F

Energy stored in a Capacitor = 1/ 2 C V2 = 1 /2 * 1.49 * 10-10 * 5502

= 22.5 * 10-6 J = 22.5 muJ

b) C = e0 A / d = (8.85 * 10-12 * 420 * 10-4 ) / (4.2 * 10-3) = 8.85 * 10-11 F

Energy stored in a Capacitor = 1/ 2 C V2 = 1 /2 * 8.85 * 10-11 * 5502

= 13.4 * 10-6 J = 13.4 muJ

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