Verified Solution • 2025–26 Session moderate

QJEEM22Ph7f0d: JEE Main 2022 Physics - Class 12 JEEM22Ph7f0d Solution: A parallel beam of light of wavelength and intensity is…

A parallel beam of light of wavelength 900 nm900 \mathrm{~nm} and intensity 100 Wm−2100 \,\mathrm{Wm}^{-2} is incident on a surface perpendicular to the beam. The number of photons crossing 1 cm21 \mathrm{~cm}^{2} area perpendicular to the beam in one second is :

Multiple Choice Options

  • A 3×10163 \times 10^{16}
  • B 4.5×10164.5 \times 10^{16}
  • C 4.5×10174.5 \times 10^{17}
  • D 4.5×10204.5 \times 10^{20}

Step-by-Step Verified Solution

λ\lambda = 900 nm

I = 100 W/m2

A = 10 −- 4

⇒\Rightarrow P = 10 −- 2 W

⇒\Rightarrow Number of photons incident per second

=10−2λhc= {{{{10}^{ - 2}}\lambda } \over {hc}}

=9×10−11×1026.63×10−34×3×108≃4.5×1016= {{9 \times {{10}^{ - 11}} \times {{10}^2}} \over {6.63 \times {{10}^{ - 34}} \times 3 \times {{10}^8}}} \simeq 4.5 \times {10^{16}}

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