6. A flat capacitor has between its plates a solid dielectric plate with a permittivity ε = 4, which completely fills the gap between them. The capacitance of the capacitor is equal to C = 50 pF. The capacitor is connected to a source with a voltage of U = 240 V. What work A must be done in order to slowly pull the dielectric plate out of the capacitor? There is no friction.

Detailed solution. Decorated in Microsoft Word 2003. (Target decided to use formula editor)