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:

Question

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: (A) 3 × 1016 (B) 9 × 1015 (C) 3 × 1019 (D) 9 × 1017

Tardigrade Admin · Accepted Answer

λ=667 × 10-9 m , P =9 × 10-3 W P =( Nhc /λ), N = No. of photons emitted /sec. N =(9 × 10-3 × 667 × 10-9/6.6 × 10-34 × 3 × 108) =3 × 1016 / sec

Q. 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:

$3 \times 1 0^{16}$

$9 \times 1 0^{15}$

$3 \times 1 0^{19}$

$9 \times 1 0^{17}$

$λ = 667 \times 1 0^{- 9} m, P = 9 \times 1 0^{- 3} W$
$P = \frac{N h c}{λ}, N =$ No. of photons emitted /sec.
$N = \frac{9 \times 1 0 ^{- 3} \times 667 \times 1 0 ^{- 9}}{6.6 \times 1 0 ^{- 34} \times 3 \times 1 0 ^{8}}$
$= 3 \times 1 0^{16} / sec$

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

3×1016

9×1015

3×1019

9×1017