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 V`. The metallic plate is slowly extraced from the gap. Find :
(a) the energy increment of the capacitor,
(b) the mechanical work performed in the process of plate extraction.

Answer

(a)`-0.15mJ` (b) `0.15mJ`