78 Capacitance and DielectricsQ26.7A capacitor stores energy in the electric field between the plates. This is most easily seen when usinga “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 capacitoris suddenly “recharged”—by induction—due to the electric field set up and “stored” in thedielectric. This proves to be an instructive classroom demonstration, especially when you ask astudent to reconstruct the capacitor without supplying him/her with any rubber gloves or otherinsulating material. (Of course, this is afterthey sign a liability waiver).Q26.8The work you do to pull the plates apart becomes additional electric potential energy stored in thecapacitor. The charge is constant and the capacitance decreases but the potential difference increasesto drive up the potential energy 12QV∆. The electric field between the plates is constant in strength
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