Question

The radiation force experienced by body exposed to radiation of intensity I(as shown in figure), assuming surface of body to be perfectly absorbing, is

• A. $\frac{4\pi R^{2}I}{c}$
• B. $\frac{\pi R^{2}I}{c}$
• C. None of these
• D. $\frac{2\pi R^{2}I}{c}$

Answer 1

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

For perfectly absorbing body radiation, force is
$F=\frac{I\times \text{Area normal to Intensity}}{\text{Speed of light}}$
$\therefore F=\frac{I\pi R^2}{c}$