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BITSAT 2021
Exam
BITSAT
Year
2021
Subject
Physics
Chapter
Dual Nature of Matter

BITSAT 2021 · Physics · Dual Nature of Matter

Monochromatic light of wavelength 667 nm is produced by a helium...

Monochromatic light of wavelength 667nm667 \mathrm{ nm} is produced by a helium neon laser. The power emitted is 9mW9 \mathrm{ mW}. The number of photons arriving per sec on the average at a target irradiated by this beam is:

Options

  1. A3×10163 \times 10^{16}
  2. B9×10159 \times 10^{15}
  3. C3×10193 \times 10^{19}
  4. D9×10179 \times 10^{17}

Correct answer

A. 3×10163 \times 10^{16}

Step-by-step solution

λ=667×10−9m,P=9×10−3WP= Nhc λ,N=\lambda=667 \times 10^{-9} m, \mathrm{P}=9 \times 10^{-3} \mathrm{ W}\mathrm{P}=\frac{\text{ Nhc }}{\lambda}, \mathrm{N}= No. of photons emitted/sec. N=9×10−3×667×10−96.6×10−34×3×108=3×1016/sec⁡\mathrm{N}=\frac{9 \times 10^{-3} \times 667 \times 10^{-9}}{6.6 \times 10^{-34} \times 3 \times 10^{8}}=3 \times 10^{16} / \mathrm\sec
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