The radii of the inner and outer spheres of a spherical capacitor are 8 cm and 9 cm respectively. The outer sphere is earthed and the inner sphere is charged. If the space between the concentric spheres is filled with a liquid of dielectric constant 5 , the capacitance of the capacitor is

A capacitor of capacitance $2 \mu \mathrm{~F}$ is charged to 50 V and then disconected from the source. Later the gap between the plates of the capacitor is filled with a dielectric material. If the energy stored in the capacitor is decreased by $25 \%$ of its initial value, then the dielectric constant of the dielectric material is

Eight capacitors each of capacity $2 \mu \mathrm{~F}$ are arranged as shown in figure. The effective capacitance between $A$ and $B$ is