A condenser of capacity $C$ is charged to a potential difference of $V_1$. The plates of the condenser are…

A condenser of capacity $C$ is charged to a potential difference of $V_1$. The plates of the condenser are then connected to an ideal inductor of inductance $L$. The current through the inductor when the potential difference across the condenser reduces to $V_2$ is
  1. $\left(\frac{\mathrm{C}\left(\mathrm{V}_1-\mathrm{V}_2\right)^2}{\mathrm{~L}}\right)^{\frac{1}{2}}$
  2. $\frac{\mathrm{C}\left(\mathrm{V}_1^2-\mathrm{V}_2^2\right)}{\mathrm{L}}$
  3. $\frac{\mathrm{C}\left(\mathrm{V}_1^2+\mathrm{V}_2^2\right)}{\mathrm{L}}$
  4. $\left(\frac{\mathrm{C}\left(\mathrm{V}_1^2-\mathrm{V}_2^2\right)}{\mathrm{L}}\right)^{\frac{1}{2}}$

Solution

\(\begin{aligned} & \frac{\mathrm{CV}^2}{2}+\frac{1}{2} \mathrm{Li}^2=\text { constant } \\ & \text { Initially } \mathrm{i}=0, \mathrm{~V}=\mathrm{V}_1 \\ & \text {Total energy }=\frac{1}{2} \mathrm{CV}_1^2 \\ & \mathrm{~When } \mathrm{V} \rightarrow \mathrm{V}_2 \\ & \frac{1}{2} \mathrm{C}\left(\mathrm{V}_2\right)^2+\frac{1}{2} \mathrm{Li}^2=\frac{1}{2} \mathrm{CV}_1^2 \\ & \mathrm{Li}^2=\mathrm{C}\left(\mathrm{V}_1^2-\mathrm{V}_2^2\right)^2 \\ & \mathrm{i}^2=\frac{\mathrm{C}}{\mathrm{L}}\left(\mathrm{V}_1^2-\mathrm{V}_2^2\right) \\ & \mathrm{i}=\sqrt{\frac{\mathrm{C}}{\mathrm{L}}\left(\mathrm{V}_1^2-\mathrm{V}_2^2\right)}\end{aligned}\) ^

Asked in: NEET 2010 (Mains)

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