P26_029 - AV 2 2 d and the nal energy stored is U f = 1 2 A...

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29. (a) Let q be the charge on the positive plate. Since the capacitance of a parallel-plate capacitor is given by ε 0 A/d , the charge is q = CV = ε 0 AV/d . After the plates are pulled apart, their separation is 2 d and the potential diFerence is V 0 .Th en q = ε 0 AV 0 / 2 d and V 0 = 2 d ε 0 A q = 2 d ε 0 A ε 0 A d V =2 V. (b) The initial energy stored in the capacitor is U i = 1 2 CV 2 =
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Unformatted text preview: AV 2 2 d and the nal energy stored is U f = 1 2 A 2 d ( V ) 2 = 1 2 A 2 d 4 V 2 = AV 2 d . This is twice the initial energy. (c) The work done to pull the plates apart is the diFerence in the energy: W = U f U i = AV 2 / 2 d ....
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