A point source of light is placed at the centre of curvature of a hemispherical surface. The source emits a power of $24 \mathrm{~W}$. The radius of curvature of hemisphere is $10 \mathrm{~cm}$ and the inner surface is completely reflecting. The force on the hemisphere due to the light falling on it is ____________ $\times~10^{-8} \mathrm{~N}$.