A \(100 \mathrm{~V}\) battery is connected across the series combination of the two capacitors of \(4 \mu…

A \(100 \mathrm{~V}\) battery is connected across the series combination of the two capacitors of \(4 \mu \mathrm{F}\) and \(8 \mu \mathrm{F}\). The energy stored in the series combination is
  1. \(0.75 \times 10^{-2} \mathrm{~J}\)
  2. \(1.33 \times 10^{-2} \mathrm{~J}\)
  3. \(0.5 \mathrm{~J}\)
  4. \(1 \mathrm{~J}\)

Solution

Potential difference across terminals of battery, \(V=100 \mathrm{~V}\)
Equivalent capacitance of series combination is given as \(\begin{aligned} & \frac{1}{C}=\frac{1}{C_1}+\frac{1}{C_2}=\frac{1}{4}+\frac{1}{8}=\frac{2+1}{8} \\ & \Rightarrow \quad \frac{1}{C}=\frac{3}{8} \Rightarrow C=\frac{8}{3} \mu \mathrm{F} \end{aligned}\) Same charge will be flow in series combination which is given as \(\begin{aligned} q & =C V=\frac{8}{3} \times 10^{-6} \times 100 \\ & =\frac{8}{3} \times 10^{-4} \mathrm{C} \end{aligned}\) \(\therefore\) Energy stored, \(E=\frac{1}{2} \frac{q^2}{C}\) \(\begin{aligned} & =\frac{1}{2} \times \frac{\left(\frac{8}{3} \times 10^{-4}\right)^2}{\frac{8}{3} \times 10^{-6}}=\frac{4}{3} \times 10^{-2} \mathrm{~J} \\ \Rightarrow E & =1.33 \times 10^{-2} \mathrm{~J} \end{aligned}\)

Asked in: AP EAMCET 2020 (21 Sep Shift 1)

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