Electromagnetism - Capacitor

A 3-microfarad capacitor is connected in series with 6-microfarad capacitor. When a 300-volt potential difference is applied across this combination, the total energy stored in the two capacitor is

A. 0.09 J
B. 0.18 J
C. 0.27 J
D. 0.41 J
E. 0.81 J
(GR0177 #10)
Solution:

C in Series:

1/Cnet  = 1/C1  + 1/C2 = ( 1/3  + 1/6 )  ( 1/10-6 ) = 1/∙ 10-6 

Cnet = 2 ∙ 10-6 

U = ½ QV = ½ CnetV2 = ½ (2 ∙ 10-6) (300)= 9 (10-6) (104) = 0.09 J

Answer: A

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