Question

In the circuit given below, the charge is $\mu C$, on the capacitor having $5\mu F$ is :

• A. $4.5$
• B. $9$
• C. $7$
• D. $15$

Answer 1

The correct option is B $9$

As capacitor 4 and combine (3,2, 5) are in parallel so potential across (3,2,5) $V=6V$
Equivalent capacitor for (3,2,5) is $C_{eq}=\frac{3(2+5)}{3+(2+5)}=2.1\mu F$
thus, $Q_{eq}=C_{eq}V=2.1\times 6=12.6\mu C$
As capacitor 3 and (2,5) are in series so charge on 3 and (2,5) is equal to $Q_{eq}$.
Net capacitance for (2,5) is $C_{(2,5)}=2+5=7\mu F$.
Thus potential across (2,5) is $V_{2,5}=\frac{Q_{eq}}{C_{(2,5)}}=\frac{12.6}{7}=1.8V$
As 2 and 5 are in parallel so potential across each is same. i,e $V_{2,5}=1.8V$
Charge on 5 is $Q_5=C_5{V}_{2,5}=5\left(1.8\right)=9\mu C$