Question

A plane light wave of intensity $I=0.20Wc{m}^{-2}$ falls on a plane mirror surface with reflection coefficient $\rho =0.8$. The angle of incident is ${45}^o$. In terms of corpuscular theory, find the magnitude of the normal pressure exerted on that surface:

• A. $1.2Nc{m}^{-2}$
• B. $0.2Nc{m}^{-2}$
• C. $2.6Nc{m}^{-2}$
• D. $0.53\times {10}^{-9}N{m}^{-2}$

Answer 1

The correct option is D $0.53\times {10}^{-9}N{m}^{-2}$

Considering the incidence at $\theta ={45}^o$ angle, the normal Pressure is given by:
$P=\frac{2Ico{s}^2\left(\theta \right)\rho }{c}$
where $c$ is the speed of light.
Now, $I=0.20Wc{m}^{-2}$
$\rho =0.8$
$c=3\times {10}^{8}m/s$
so the Pressure, $P=0.53\times {10}^{-9}N{m}^{-2}$