Question

A plane electromagnetic wave of intensity of $10\, W / m ^{2}$ strikes a small mirror of area $20\, cm ^{2}$, held perpendicular to the approaching wave. The radiation force on the mirror will be

• A. $6.6 \times 10^{-11} N$
• B. $1.33 \times 10^{-11} N$
• C. $1.33 \times 10^{-10} N$
• D. $6.6 \times 10^{-10} N$

Answer 1

Answer: (C)

Radiation force = momentum transferred per second by electromagnetic wave to the mirror
$=\frac{2 S_{a v} A}{c}=\frac{2 \times(10) \times\left(20 \times 10^{-4}\right)}{\left(3 \times 10^{8}\right)}$
$=1.33 \times 10^{-10} N$