Question

How to solve? What is different when switch is closed?Help!

Answer 1

When the switch `S` will be closed, both the capacitors will try to discharge,but see the polarity of the two capacitors,they are against the direction of each other,that means `C1` tries to charge `C2` and `C2` tries to charge `C1`.

But, that can't happen,only the one with higher volatge will charge the capacitor at lower volatge,untill the volatage difference across them becomes equal.

Now,let total charge contributed by the two capacitors will be constant

So, `Q = q1+q2`

or, `VC = V1C1 +V2C2` (where `V` is the final common volatge across both the capacitance, and `C` is the equivalent capacitane of the circuit i.e `5 muF` as both are in parallel combination)

So, `V*5 = 12*3 +6*2`

or, `V= 9.6 vo l t`