Question

Two condensers of capacity C and 2C are connected in parallel and these are charged uptoV volt. If the battery is removed and dielectric medium of constant K is put between the plates of first condenser, then the potential at each condenser is

• A. $\frac { V } { K + 2 }$
• B. $2 + \frac { K } { 3 V }$
• C. $\frac { 2 V } { K + 2 }$
• D. $\frac { 3 V } { K + 2 }$

Answer 1

Answer: (D)

$\frac { 3 V } { K + 2 }$

Answer 2

Initially

Equivalent capacitance of the system $C _ { e q } = 3 C$

Finally

Equivalent capacitance of the system $C _ { e q } = K C + 2 C$

Hence common potential

$V = \frac { Q } { ( K C + 2 C ) } = \frac { 3 C V } { ( K + 2 ) C } = \frac { 3 V } { K + 2 }$.