A parallel plate capacitor of capacitance $C$ is connected to a battery and is charged to a potential difference $V$. Another capacitor of capacitance $2C$ is similarly charged to a potential difference $2V$. The charging battery is now disconnected and the capacitors are connect in parallel to each other in such a way that the positive terminal of one is connected to the negative terminal of the other. The final energy of the configuration is
Medium
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As both capacitors are in parallel so equivalent capacitance $C_{e q}=C+2 C=3 C$
Net potential, $V_{n}=2 V-V=V$
Energy stored, $U=\frac{1}{2} C_{e q} V_{n}^{2}=(1 / 2) \times 3 C V^{2}=\frac{3}{2} C V^{2}$
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