How many photons of wavelength $\lambda = 6600 \ nm$ must strike a totally reflecting screen per second at normal incidence so as to exert a force of $1 \ \mu N$?

If the radiant energy received from an electric bulb per second is $25 \ J/s$ and the velocity of electromagnetic waves is $c = 3 \times 10^8 \ m/s$,then the force exerted on the surface in one second is:

$A$ 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 the hemisphere is $10 \, cm$ and the inner surface is completely reflecting. The force on the hemisphere due to the light falling on it is $.......... \times 10^{-8} \, N$.

$50\, W/m^2$ energy density of sunlight is normally incident on the surface of a solar panel. Some part of incident energy $(25\%)$ is reflected from the surface and the rest is absorbed. The force exerted on $1\, m^2$ surface area will be close to $(c = 3 \times 10^8\, m/s)$.

Light falls on a non-reflecting surface normally. If the average force exerted on a surface with area $15 \text{ cm}^2$ during a $20 \text{ minute}$ time interval is $10^{-6} \text{ N}$,then the energy flux (intensity) of light is (Velocity of light $= 3 \times 10^8 \text{ ms}^{-1}$)

The radiation of energy $E$ falls normally on a perfectly reflecting surface. The momentum transferred to the surface is