Dual Nature of Radiation and Matter - Result Question 42
44. 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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======= ####44. 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:
c3eec34ec6b1fad69db54a20ad4b2dca40c2aa54 (a) $3 \times 10^{16}$
(b) $9 \times 10^{15}$
(c) $3 \times 10^{19}$
(d) $9 \times 10^{17}$
[2009]
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Answer:
Correct Answer: 44. (a)
Solution:
- (a) $\lambda=667 \times 10^{-9} m, P=9 \times 10^{-3} W$
$P=\frac{Nhc}{\lambda}, N=$ No. of photons emitted $/ sec$.
$N=\frac{9 \times 10^{-3} \times 667 \times 10^{-9}}{6.6 \times 10^{-34} \times 3 \times 10^{8}}$
$=\frac{9 \times 6.67 \times 10^{-10}}{3 \times 6.6 \times 10^{-26}} \simeq 3 \times 10^{16} / sec$
