A spherical capacitor has an inner sphere of radius $12\;cm$ and an outer sphere of radius $13\;cm$. The outer sphere is earthed and the inner sphere is given a charge of $2.5\;\mu C$. The space between the concentric spheres is filled with a liquid of dielectric constant $32$. Compare the capacitance of this capacitor with that of an isolated sphere of radius $12\;cm$. Explain why the latter is much smaller.