Question

Consider a sphere of radius $R$ exposed to radiation of intensity $I$ as shown in figure. If surface of sphere is partially reflecting with reflection coefficient is $0.3$, then radiation force experienced is

• A. $\frac{0.3\pi R^{2}I}{c}$
• B. $\frac{1.3\pi R^{2}I}{c}$
• C. $\frac{1.7\pi R^{2}I}{c}$
• D. $\frac{\pi R^{2}I}{c}$

Answer 1

The correct option is B $\frac{1.3\pi R^{2}I}{c}$

Given, reflection coefficient, $\alpha =0.3$

The total radiation force acting on the sphere is,

$F_R=\frac{(1+\alpha )IA}{c}$

Where, $A=\pi R^2=\text{Effective area}$

$F_R=\frac{(1+0.3)I\pi R^2}{c}=\frac{1.3I\pi R^2}{c}$

Hence, $\left(D\right)$ is the correct answer.