Question

The Sun delivers ${10}^{3}W/m^2$ of electromagnetic flux to the Earth's surface. The radiation force on the roof of dimensions $8m\times 20m$ will be:

• A. $3.33\times {10}^{-5}N$
• B. $5.33\times {10}^{-4}N$
• C. $7.33\times {10}^{-3}N$
• D. $9.33\times {10}^{-2}N$

Answer 1

The correct option is B $5.33\times {10}^{-4}N$

Poynting vector, $S={10}^{3}W/m^2$
Pressure, $P=\frac{S}{c}=$$\frac{1000}{3\times {10}^8}$
$=3.33\times {10}^{-6}N/m^2$
Radiation force on the roof is given by:
$F=P\times 8\times 20=5.33\times {10}^{-4}N$