Question

Three capacitors $3\, \mu F , 6 \, \mu F$ and $6\, \mu F$ are connected in series to a source of $120 \, V$. The potential difference, in volt, across the $3 \, \mu F$ capacitor will be

• A. 24
• B. 30
• C. 40
• D. 60

Answer 1

Answer: (D)

60

Answer 2

The combination of three charges in series $\frac{1}{C}=\frac{1}{C_{1}}+\frac{1}{C_{2}}+\frac{1}{C_{3}}$ $\frac{1}{C}=\frac{1}{3}+\frac{1}{6}+\frac{1}{6}$ $\Rightarrow C=\frac{6}{4}=1.5\, \mu F$ The charge of this circuit $q=C V=1.5 \times 120$ $q=180\, \mu C$ The potential difference across the $3\, \mu F$ $q=C \,V$ $V=\frac{q}{C}=\frac{180}{3}=60\, V$