this question is answered in this link but there is something I don\'t understan

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this question is answered in this link but there is something I don't understand http://www.chegg.com/homework-help/questions-and-answers/30-f-capacitor-charged-40-v-50-fcapacitor-charged-18-v-connected-thepositive-plate-connect-q789919 "A 3.0-F capacitor charged to 40 V and a 5.0-F capacitor charged to 18 V are connected to each other, with the positive plate of each connected to the negative plate of the other. What is the final charge on the 3.0-F capacitor? shoe steps. The capacitors aren't connected at first right? then they are connected. Are they connected in series or in parallel and how do I know?

Explanation / Answer

Q1 = charge stored 0n 3 uF capacitor = 3 x 40 = 120 uC

Q2 = charge stored 0n 5 uF capacitor = 5 x 18 = 90 uC

the capacitors are connected in parallel

hence net total capacitance = C = C1 + C2 = 3 + 5 = 8 uF

net charge = 120 - 90 = 30 uC

common potential = V = Q/C = 30/8 = 3.75 volts

new charge on C1 = Q' = C1V = 3 x 3.75 = 11.25 uF

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