Question

Two metal plates having charges Q, −Q face each other at some separation and are dipped into an oil tank. If the oil is pumped out, the electric field between the plates will
(a) increase
(b) decrease
(c) remain the same
(d) become zero.

Answer 1

(a) increase

Oil between the plates of the capacitor acts as a dielectric. We know that the electric field decreases by a factor of $\frac{1}{K}$ of the original field when we insert a dielectric between the plates of a capacitor (K is the dielectric constant of the dielectric). So, if the oil is pumped out, the electric field between the plates will increase, as the dielectric has been removed.