NOW  MY TEACHER TOLD ME THAT THOUGH S2 IS CLOSED UNLESS U CONNECT THE CAPACITORS C1 AND C2 AND MAKE IT A CLOSED CIRCUIT NO CHARGE REDISTRIBUTION TAKES PLACE THAT IS BOTH THE CAPACITORS REMAIN AT THE SAME POTENTIAL  30V AND 20V RESPECTIVELY .

NOW EARLIER I HAD SOLVED A PROBLEM WHERE TWO DIFFERENT SPHERICAL CONDUCTORS OF DIFFERENT CAPACITIES SAY C1 AND C2 , WERE CHARGED TO POTENTIALS V1 AND V2 RESPECTIVELY WERE CONNECTED BY A LONG WIRE AND CHARGE REDISTRIBUTION TAKES  PLACE  AND THE COMMON POTENTIAL OF THE TWO WERE CALCULATED .

HERE AS WELL U HAVE TWO CAPACITORS CONNECTED TO EACH OTHER THEN WHY DOES IT NOT COME TO A COMMON POTENTIAL ?? THAT IS I EXPECT V1'/V2' = C2/C1

PLEASE EXPLAIN THANK YOU

Current/charge never flows if the circuit is not completed.

For a moment, lets assume that the circuit is incomplete and as the +ve and -ve plates are connected, the charge flows(fig. 1). After the charge has flows, these 2 plates get neutralised.

But what abt the other plates of the 2 capacitors which are not connected(fig 2). They still have that charge. And even though their partner plates' charge was neutralised, the charge wud again get induced due to the charge on these plates(fig 3). So, no net charge flows.

Now, consider that circuit is complete(fig 4). Now, both the plates of both the capacitors are connected and both of them can get neutralised(fig 5). So, some net charge flows thru the circuit.

In case of spherical capacitors, we consider the other plate of a capacitor to be at infinity, so they are assumed to be connected.

Hope u get it.