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azure kitsune
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Homework Statement
A 1.00 micro-F capacitor charged to 50.0 V and a 2.00 micro-F capacitor charged to 20.0 V are connected, with the positive plate of each connected to the negative plate of the other. What is the final charge on the 1.00 micro-F capacitor?
Homework Equations
Q = CV
The Attempt at a Solution
Let a subscript of 1 denote the 1.00 micro-F capacitor, and a subscript of 2 denote the other.
Intially:
Q1 = C1V1 = 50 micro-C
Q2 = C2V2 = 40 micro-C
When the two capacitors are connected together, the first one has charge Q1' and the second has charge Q2' with:
Q1' + Q2' = 50 - 40 = 10 micro-C
The total potential drop around the loop must be zero, so we have
V1' = V2'
so
Q1'/C1 = Q2'/C2
Then when I solve for Q1', I get 3.3 micro-C, which is wrong. The correct answer according to the textbook is 45 micro-C.