A parallel plate capacitor has plate area $50 \mathrm{~cm}^2$ and plate separation 3 mm . The space between the plates is filled with a dielectric medium of thickness 1 mm and dielectric constant 4 . The capacitance becomes ( $\varepsilon_0=$ permittivity of free space)

The equivalent capacitance between plates ' A ' and ' B ' ( A -area of each plate, d-separation between plates) ( $\varepsilon_0$ - permittivity of free space) is

The voltage between the plates of a parallel plate capacitor of capacity $1 \mu \mathrm{~F}$ is changing at the rate of $4 \mathrm{~V} / \mathrm{s}$. the displacement current in the capacitor is

A parallel plate air capacitor has capacitance $C_P$. It is equally filled with parallel layers of materials of dielectric constants $\mathrm{K}_1$ and $\mathrm{K}_2$. Now its capacity becomes $C_K$. The ratio $C_P$ to $C_K$ is