Question

Light with an energy flux of $25\times {10}^{4}w{m}^{-2}$ falls on a perfectly reflecting surface at normal incidence. If the surface area is $15c{m}^2$, 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. $3.0\times {10}^{-6}N$

Answer 1

The correct option is B $2.50\times {10}^{-6}N$

$F=\frac{2IA}{C}=\frac{2(25\times {10}^4)(15\times {10}^{-4})}{3\times {10}^8}=2.5\times {10}^{-6}N$