Question 115: Dual Nature of Matter and Radiation

Question

A parallel beam of light of wavelength $$900 \mathrm{~nm}$$ and intensity $$100 \,\mathrm{Wm}^{-2}$$ is incident on a surface perpendicular to the beam. The number of photons crossing $$1 \mathrm{~cm}^{2}$$ area perpendicular to the beam in one second is :

Accepted Answer

$$\lambda$$ = 900 nm
I = 100 W/m
2
A = 10
$$-$$4
$$\Rightarrow$$ P = 10
$$-$$2
W
$$\Rightarrow$$ Number of photons incident per second
$$ = {{{{10}^{ - 2}}\lambda } \over {hc}}$$
$$ = {{9 	imes {{10}^{ - 11}} 	imes {{10}^2}} \over {6.63 	imes {{10}^{ - 34}} 	imes 3 	imes {{10}^8}}} \simeq 4.5 	imes {10^{16}}$$

Answer

$$3 	imes 10^{16}$$

Answer

$$4.5 	imes 10^{16}$$

Answer

$$4.5 	imes 10^{17}$$

Answer

$$4.5 	imes 10^{20}$$

Dual Nature of Matter and Radiation

A parallel beam of light of wavelength $900 \mathrm{~nm} and intensity 100 \,\mathrm{Wm}^{-2} is incident on a surface perpendicular to the beam. The number of photons crossing 1 \mathrm{~cm}^{2}$ area perpendicular to the beam in one second is :

Choose the correct answer: