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Solve Problem 25.7 assuming that the plates remain connected to the voltage source. |
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Answer» Solution :In this case, too, the capacitance of the capacitor increases as the LIQUID rises, but the energy of the ELECTRIC field is not conserved but increases. Besides, the potential energy of the rising water increases as well. Is this not in contradiction with the LAW of conservation of energy? Of course not. The power supply PERFORMS work to raise the liquid, the increase in the energy of the system being equal to the work of the power supply in displacing the charges to the capacitor plates: `W_(p.s)=DeltaW_(el)+Delta_("pot")` But `W_(p.s)=Deltaq. varphi=(C-C_(0))varphi^(2)` Substituting, we obtain the result sought after some simple transformations. |
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