Question 81: EM waves

Question

Sun light falls normally on a surface of area $$36 \mathrm{~cm}^{2}$$ and exerts an average force of $$7.2 	imes 10^{-9} \mathrm{~N}$$ within a time period of 20 minutes. Considering a case of complete absorption, the energy flux of incident light is

Accepted Answer

Pressure $$ = {l \over c}$$
$$ \Rightarrow {F \over A} = {l \over c}$$
$$ \Rightarrow l = {{7.2 	imes {{10}^{ - 9}} 	imes 3 	imes {{10}^8}} \over {36 	imes {{10}^{ - 4}}}}$$ W/m
2
$$ = 600$$ W/m
2
$$ \Rightarrow l = 0.06$$ W/cm
2

Answer

$$25.92 	imes 10^{2} \mathrm{~W} / \mathrm{cm}^{2}$$

Answer

$$8.64 	imes 10^{-6} \mathrm{~W} / \mathrm{cm}^{2}$$

Answer

$$6.0 \mathrm{~W} / \mathrm{cm}^{2}$$

Answer

$$0.06\mathrm{~W} / \mathrm{cm}^{2}$$

EM waves

Sun light falls normally on a surface of area $36 \mathrm{~cm}^{2} and exerts an average force of 7.2 \times 10^{-9} \mathrm{~N}$ within a time period of 20 minutes. Considering a case of complete absorption, the energy flux of incident light is

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