Question

In which of the following cases, the force due to the incident radiation will be largest? Assume same intensity and surface area for all cases.

$\left(1\right)$ Radiation incident normally on a surface, getting absorbed completely.

$\left(2\right)$ Radiation incident normally on a surface, getting reflected completely and travelling in opposite direction with same speed.

$\left(3\right)$ Radiation incident obliquely on a surface, getting reflected completely and travelling with same speed, after reflection.

• A. Case $\left(1\right)$
• B. Case $\left(2\right)$
• C. Case $\left(3\right)$
• D. Force will be the same in all cases.

Answer 1

The correct option is B Case $\left(2\right)$

The force exerted on the surface, in each of the given cases, will be as follows.

$\left(1\right)$ $F=\frac{IA}{c}$



$\left(2\right)$
$F=\frac{2IA}{c}$


$\left(3\right)$
$F=\frac{IA{\cos }^2\theta }{c}$

From the three equations, it is clear that the force will be maximum in case $\left(2\right)$

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