A plane light wave of intensity `I = 0.20 W//cm^(2)` falls on a plane mirror surface with reflection coefficient `rho = 0.8`. The angle of incidence is `45^(@)`. In terms of the corpuscular theory find the magnitude of the normal pressure extered by light on that surface.

Explanation

Suppose the mirror has a surtace area `A`.
The incident beam then has a cross section of `A cos theta` and the incident enegry is `IA cos theta`: Then the momentum transferred per second `(=` Force) is from the lest problem `-(IA cos theta)/(c ) (1+rho)cos theta hatj +(IA cos theta)/(c ) (1-rho)sin theta hati` The normal pressure is then `p = (I)/(c)(1+rho)cos^(2)theta (hatj` is the unit vector `_|_^(r )` to the plane mirror). Putting in the values
`p = (0.20xx10^(4))/(3xx10^(8)) xx1.8 xx (1)/(2) = 0.6nNcm^(-2)`