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NEET 2009
Exam
NEET
Year
2009
Subject
Physics
Chapter
Dual Nature of Matter

NEET 2009 · Physics · Dual Nature of Matter

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

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

Options

  1. A9×10179 \times 10^{17}
  2. B3×10163 \times 10^{16}
  3. C9×10159 \times 10^{15}
  4. D3×10193 \times 10^{19}

Correct answer

B. 3×10163 \times 10^{16}

Step-by-step solution

Here λ=667×10−9m,P=9×10−3W\lambda=667 \times 10^{-9} \mathrm{ m}, \mathrm{P}=9 \times 10^{-3} \mathrm{ W} Power = energy  time =nhcλt=Nhcλ\begin{aligned} \text{ Power } & =\frac{\text{ energy }}{\text{ time }} \\ & =\frac{n h c}{\lambda \mathrm{t}} \\ & =\frac{N h c}{\lambda} \end{aligned}whereisnumberwhere is number of photonsemittedpersec.photons emitted per sec.⇒N=P×λhc=9×10−3×667×10−96.6×10−34×3×108=3×1016/s\begin{aligned} \Rightarrow \quad \mathrm{N} & =\frac{\mathrm{P} \times \lambda}{\mathrm{hc}} \\ & =\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{s} \end{aligned}$$
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