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Question

Physics Question on Photoelectric Effect

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

A

3×10163\times 10^{16}

B

9×10159\times 10^{15}

C

3×10193\times 10^{19}

D

9×10179\times 10^{17}

Answer

3×10163\times 10^{16}

Explanation

Solution

No. of photons =E( hc /λ)=\frac{E}{(\text { hc } / \lambda)} =9×10−3×6.67×10−76.6×10−34×3×108=\frac{9 \times 10^{-3} \times 6.67 \times 10^{-7}}{6.6 \times 10^{-34} \times 3 \times 10^{8}} =3×1016=3 \times 10^{16}