Question

A radiation of $200W$ is incident on a surface which is $60$% reflecting and $40$% absorbing. Find the net Force acting on the surface.

• A. $1.3\times {10}^{-6}N$
• B. $1.07\times {10}^{-6}N$
• C. $1.07\times {10}^{-7}N$
• D. $1.3\times {10}^{-7}N$

Answer 1

Answer: (B)

$1.07\times {10}^{-6}N$

For absorbing bodies, force $F_{abs}=P_1/c$ and for reflecting bodies , $F_{ref}=2P_2/C$ where $P_1=$amount of power absorb , $P_2=$amount of power reflect and c = velocity of light.

Total force , $F_{tot}=F_{abs}+F_{ref}=\frac{0.4P}{c}+\frac{2\left(0.6\right)P}{c}=\frac{1.6P}{c}=\frac{1.6\times 200}{3\times {10}^8}=1.07\times {10}^{-6}N$