Question

Two capacitors of capacity $6\mu F$ and $3\mu F$ are charged to $100V$ and $50V$ separately and connected as shown in figure. Now all the three switches $S_1,S_2$ and $S_3$ are closed. Which plates form an isolated system?

• A. plate $1$ and plate $4$ separately
  
• B. plate $2$ and plate $3$ separately
• C. plate $2$ and plate $3$ jointly
• D. none of these

Answer 1

The correct option is C plate $2$ and plate $3$ jointly

Isolated system: In an isolated system net charge remains constant (if it is not connected to either of the terminals of a battery or to the earth)
As plate $1$ and $4$ are connected to battery terminals they are not isolated system
But plates $2$ and $3$ are neither connected to battery nor to the earth so net charge remains constant jointly
Answer $C$ plate $2$ and Plate $3$ jointly