A capacitor of capacitance Ck is charged to a potential difference V0. The termi

Question

A capacitor of capacitance Ck is charged to a potential difference V0. The terminals of the charged capacitor are then disconnected from the power supply and connected to terminals of an uncharged capacitor of capacitance Cu.

(a) Find the original charge of the system. Express your answer in terms of the variables Ck and V0. (b) Find the final potential difference across Ck. Express your answer in terms of the variables Ck, Cu and V0. (c) What the final potential difference across Cu. Express your answer in terms of the variables Ck, Cu and V0. (d) Derive the formula you used in Capacitance lab to find Cu.

So for a) I got Q= Ck*V0

b and c confuses me, aren't they the same thing [U = 1/2 * (Ck*V0)/Cu]? or is it something I'm missingplease explain

Explanation / Answer

a) Original charge is     definitely Ck*V0

b) when both the capacitors are connected, the potential difference between thwm is same, let it be as V.

                So, charge on Ck         q1 = V*Ck

                      charge on Cu         q2 = V*Cu

But total charge is conserved so,

                                         q1 + q2 = Ck*V0

                                      V(Ck+Cu) = CkV0

                                           V         = CkV0/(Ck+Cu)          Ans.

c) Potential difference across Cu will be same as that across Ck that is CkV0/(Ck+Cu)

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