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Electric Current

Problem 3.200

Between the plates of a parallel-plate capacitor there is a metallic plate whose thickness takes up \(\eta=0.60\) of the capacitor gap. When that plate is absent the capacitor has a capacity \(C\) \(=20\) nF. The capacitor is connected to a dc voltage source \(V\) \(=100 \mathrm{~V}\). The metallic plate is slowly extracted from the gap. Find: (a) the energy increment of the capacitor; (b) the mechanical work performed in the process of plate extraction.

Reveal Answer
 3.200. (a) ΔW=1/2CV2η/(1η)=0.15 mJA==1/2CV2η/(1η)=0.15 mJ\begin{aligned} &\text { 3.200. (a) } \Delta W=-1 / 2 C V^{2} \eta /(1-\eta)=-0.15 \quad \mathrm{~mJ}\\ &A=\\ &=1 / 2 C V^{2} \eta /(1-\eta)=0.15 \mathrm{~mJ} \end{aligned}