Q116 / 155 · WBJEE 2016 · Physics
Equivalent capacitance between $A$ and $B$ in the figure is 

- A$20 \mu \mathrm{F}$
- Correct answerB$8 \mu \mathrm{F}$
- C$12 \mu \mathrm{F}$
- D$16 \mu \mathrm{F}$
Solution
$\frac{1}{C}=\frac{1}{C_{1}}+\frac{1}{C_{2}}=\frac{1}{4}+\frac{1}{4}=\frac{2}{4}$
$C=2 \mu F$
$2 \mu \mathrm{F}$ will be parallel to $4 \mu \mathrm{F}$. so the resultant capacitance
$\begin{aligned} \frac{1}{C^{\prime \prime}} &=\frac{1}{4 \mu F}+\frac{1}{4 \mu F}=\frac{2}{4} \mu F \\ C^{-} &=2 \mu F \\ C_{A Q} &=2 \mu F+6 \mu F \\ &=8 \mu F \end{aligned}$
$\begin{aligned} \frac{1}{C^{\prime \prime}} &=\frac{1}{4 \mu F}+\frac{1}{4 \mu F}=\frac{2}{4} \mu F \\ C^{-} &=2 \mu F \\ C_{A Q} &=2 \mu F+6 \mu F \\ &=8 \mu F \end{aligned}$Hence, the correct answer is option: 'B'.