An air core parallel plate capacitor has capacitance C. It is completely filled with a dielectric slab having dielectric constant 2 K. The capacitor is now connected to a battery of emf V. It was planned to replace the dielectric slab of the capacitor while it remains connected to the battery. Another dielectric slab (which fits exactly between the plates) is inserted slowly so as to push out the earlier slab. The new slab has a dielectric constant K [see Figure (a) to (c)]
(a) By energy considerations calculate the mechanical work that must be done against the electric forces in order to complete the process.
(b) Looking at the expression of mechanical work obtained in (a), tell what was the direction of force applied by the external agent - from left to right (as indicated by `F_(1)` in Figure) or from right to left (as indicated by `F_(2)`).
(c) Which dielectric slab experienced higher force of attraction from the capacitor plates during the process ?

Answer

(a) `(1)/(2) KCV^(2)`
(b) In the direction indicated by `vec(F)_(1)`
(c) Dielectric having constant 2K experienced higher force