Question

The pressure exerted by an electromagnetic wave of intensity $I\left(W/m^2\right)$ on a non-reflecting surface is: $[c$ is the velocity of light $]$

• A. $Ic$
• B. $I{c}^2$
• C. $I/c$
• D. $I/c^2$

Answer 1

Answer: (C)

Force per unit area is the radiation pressure. When a surface intercepts electromagnetic radiation, a force and a pressure are exerted on the surface.
As the surface is non-reflecting, so, it is completely absorbed and in such case the force is,
$F=\frac{IA}{c}$
where $I$ is intensity of light. $A$ is area of surface and $c$ is velocity of electromagnetic wave.
The radiation pressure is the force per unit area
i.e., $P=\frac{F}{A}=\frac{I}{C}$