Q. Light with an energy flux of $25 \times 10^4$ $Wm^{-2}$ falls on a perfectly reflecting surface at normal incidence. If the surface area is 15 $cm^2$, the average force exerted on the surface is :
A) $1.25 \times 10^{-6}$ N
B) $2.50 \times 10^{-6}$ N
C) $1.20 \times 10^{-6}$ N
D) $3.0 \times 10^{-6}$ N
Explanation
[Solution] $F = \frac{2IA}{c} = \frac{2 \times 25\times10^4 \times 15\times10^{-4}}{3\times10^8} = 2.5 \times 10^{-6}$ N. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.