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8.Electromagnetic waves
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A plane electromagnetic wave of wave intensity $6\,W/m^2$ strike a small mirror of area $30\,cm^2$ , held perpendicular to a approching wave. The momentum transmitted in $kg\, m/s$ by the wave to the mirror each second will be
A
$1.2 \times 10^{-10}$
B
$2.4 \times 10^{-9}$
C
$3.6 \times 10^{-8}$
D
$4.8 \times 10^{-7}$
Solution
Momentum imparted per second = Force $(\mathrm{F})$
Force $=$ (Pressure) Area
$\Rightarrow \mathrm{F}=\mathrm{P}(\mathrm{A})=\mathrm{F}=\frac{2 \mathrm{I}}{\mathrm{C}} \mathrm{A}$
$F=\frac{2 \times 6 \times 30 \times 10^{-4}}{3 \times 10^{8}}$
$\Rightarrow \mathrm{F}=1.2 \times 10^{-10} \mathrm{\,Kg} \mathrm{m} / \mathrm{s}$
Standard 12
Physics
