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NEET 2009 (AIPMT) · Photons: Energy, Momentum & Radiation Pressure

Photons: Energy, Momentum & Radiation Pressure question from NEET 2009 (AIPMT)

Q35NEET 2009 · AIPMTEasy

Photons: Energy, Momentum & Radiation Pressure

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

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Answer: (a)

  1. E=hcλ=(6.63×10−34)(3×108)667×10−9≈2.98×10−19 JE = \frac{hc}{\lambda} = \frac{(6.63 \times 10^{-34})(3 \times 10^{8})}{667 \times 10^{-9}} \approx 2.98 \times 10^{-19}\text{ J}
  2. n=PE=9×10−32.98×10−19≈3×1016 s−1n = \frac{P}{E} = \frac{9 \times 10^{-3}}{2.98 \times 10^{-19}} \approx 3 \times 10^{16}\text{ s}^{-1}
  3. So the answer is (a) 3×10163 \times 10^{16}.
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