Q.

In the circuit shown below, the switch S is connected to position P for a long time so that the charge on the capacitor becomes q1 μC. Then S is switched to position Q. After a long time, the charge on the capacitor is q2 μC.

Q.   The magnitude of q1 is ______.                    [2021]


Ans.

(1.33)

When the switch is connected to position P

From KVL,

VA-1·i1-1+2-2i1=VA⇒3i1=1              ∴  i1=13 A

Again, VA-1·i1-1=VB   or,  VA-VB=1+i1=43 V

Potential drop across the capacitor,  ΔV=43 V

∴  Charge on capacitor,    q1=CΔV=1×43 μC

        q1=1.33 μC

When the switch is connected to position Q

From KVL,

VA-1·i2+2-2i2=VA⇒3i2=2        ∴  i2=23A

Again,  VA-i2×1=VB

   VA-VB=i2×1=23V

Potential difference across the capacitor, ΔV=23 V

∴  Charge on capacitor,    q2=CΔV=1×23 μC

q2=0.67 μC