Question

Light of intensity $I$ is incident on a fixed plane surface at an angle ${30}^0$ with normal to the surface. If 50 % light is reflected and remaining light is absorbed then radiation pressure on the plate is: [Speed of light is c]

• A. $\frac{2I}{c}$
• B. $\frac{3I}{8c}$
• C. $\frac{9I}{8c}$
• D. $\frac{I}{4c}$

Answer 1

Answer: (C)

$\frac{9I}{8c}$

Intensity of light polarized in the direction ${30}^{\circ }$ to the incident direction=$Ico{s}^2\theta =\frac{3I}{4}$

Now $\frac{3I}{4}\times \frac{1}{2}$ is absorbed and $\frac{3I}{4}\times \frac{1}{2}$ is reflected.

Thus radiation pressure=$\frac{1}{c}(\frac{3I}{8}-(-\frac{3I}{4}\left)\right)=\frac{9I}{8c}$