Charged capacitor connected to an uncharged capacitor

Bolter · May 12, 2020

Hi there, tried doing this question but not sure if what I did for part b is right?

Printed homework Question 5: a 2 µF capacitor charged to 12 V is disconnected and connected across an uncharged 4 µF capacitor, with parts (a) and (b) asking for the charge and the potential difference.

Handwritten working on paper: a) Q = CV, Q = (2x10^-6)(12) = 2.4x10^-5 C; b) To equilibrium, Q0 = Q1 + Q2, C1V0 = C1V + C2V, V = C1V0/(C1+C2) = 2.4x10^-5/((2+4)x10^-6) = 4V.

Appreciate any help! Thanks

Merlin3189 · May 12, 2020

Yes. Fine.

As it's so simple (the numbers), you might like to do an intuitive check and say something like,
The 4 μF is double the 2 μF, so its like you end up with 3 caps of 2 μF in parallel sharing the same charge.
So each cap has 1/3 of the total charge and so must be charged to 1/3 of the voltage that the single 2 μF needed.

Charged capacitor connected to an uncharged capacitor

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