A parallel-plate capacitor of width w, length L, and separation d has a solid dielectric s...

A parallel-plate capacitor of width w, length L, and separation d has a solid dielectric slab of permittivity E in the space between the plates. The capacitor is charged to a voltage V0by a battery, as indicated in Fig. Assuming that the dielectric slab is withdrawn to the position shown, determine the force acting on the slab

a) with the switch closed,

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b) after the switch is first opened.

Figure: A partially filled parallel-plate capacitor