What is the momentum of a photon having frequency $1.5 \times {10^{13}}Hz$

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

A convex lens of focal length $40 \mathrm{~cm}$ forms an image of an extended source of light on a photoelectric cell. A current I is produced. The lens is replaced by another convex lens having the same diameter but focal length $20 \mathrm{~cm}$. The photoelectric current now is:

Monochromatic light of frequency $6 \times 10^{14} \mathrm{~Hz}$ is produced by a laser. The power emitted is $2 \times 10^{-3} \mathrm{~W}$. How many photons per second on an average, are emitted by the source?

(Given $\mathrm{h}=6.63 \times 10^{-34} \mathrm{Js}$ )

The momentum of a photon of energy $h\nu $ will be