A solid sphere of uniform density and radius $r$ applies a gravitational force of attraction equal to $F_1$on a particle placed at $P$, distance $2R$ from the centre $O$ of the sphere. A spherical cavity of the radius $\raisebox{1ex}{$R$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$ is now made in the sphere as shown in the figure. The sphere with cavity now applied a gravitational force $F_2$ on the same particle placed at $P$. The ratio $\raisebox{1ex}{$F_2$}\!\left/ \!\raisebox{-1ex}{$F_1$}\right.$ will be