738_Physics ProblemsTechnical Physics

738_Physics ProblemsTechnical Physics - 78 Capacitance and...

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78 Capacitance and Dielectrics Q26.7 A capacitor stores energy in the electric field between the plates. This is most easily seen when using a “dissectable” capacitor. If the capacitor is charged, carefully pull it apart into its component pieces. One will find that very little residual charge remains on each plate. When reassembled, the capacitor is suddenly “recharged”—by induction—due to the electric field set up and “stored” in the dielectric. This proves to be an instructive classroom demonstration, especially when you ask a student to reconstruct the capacitor without supplying him/her with any rubber gloves or other insulating material. (Of course, this is after they sign a liability waiver). Q26.8 The work you do to pull the plates apart becomes additional electric potential energy stored in the capacitor. The charge is constant and the capacitance decreases but the potential difference increases to drive up the potential energy 1 2 QV . The electric field between the plates is constant in strength
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