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## Homework Statement

Capacitors A and B are identical. Capacitor A is charged so it stores 4J of energy and capacitor B is uncharged. The capacitors are then connected in parallel. The total stored energy in the capacitors is now ____.

## Homework Equations

U = q^2/2C

## The Attempt at a Solution

Ok, I'm not sure if this is allowed.. I already know the answer is 2J. My professor gave us an answer key with the problem done out, but I don't understand what is happening. I'm not sure where 2J went. It says 2J of energy were required to move charge from the charged capacitor to the uncharged one.

I know initial potential of A is 4J, and initial potential of B is 0. For final potential, she has U_final = q^2/2C = 1/2*q^2/2C. Where did the second 1/2 come from?

I would really appreciate some clarification.. I'm really confused.