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

Light with an energy flux of $18 \; W/cm^2$ falls on a non-reflecting surface at normal incidence. If the surface has an area of $20 \; cm^2$,find the average force exerted on the surface during a $30$ minute time span.

The number of photons falling per second on a completely darkened plate to produce a force of $6.62 \times 10^{-5} \ N$ is $n$. If the wavelength of the light falling is $5 \times 10^{-7} \ m$,then $n = \_ \times 10^{22}$. (Given: $h = 6.62 \times 10^{-34} \ J \cdot s$)

$A$ radiation of energy $E$ falls normally on a perfectly reflecting surface. The momentum transferred to the surface is ($C =$ velocity of light).

$A$ parallel beam of light is incident normally on a plane surface absorbing $50\%$ of the light and reflecting the rest. If the incident beam carries $90 \text{ W}$ of power,the force exerted by it on the surface is ($C = 3 \times 10^8 \text{ m/s}$ is the velocity of light in air).

$A$ beam of white light is incident normally on a plane surface absorbing $70 \%$ of the light and reflecting the rest. If the incident beam carries $10 \ W$ of power,the force exerted by it on the surface is