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

No. of photons =(E/( text hc / λ)) =(9 × 10-3 × 6.67 × 10-7/6.6 × 10-34 × 3 × 108) =3 × 1016

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

$3 \times 1 0^{16}$

$9 \times 1 0^{15}$

$3 \times 1 0^{19}$

$9 \times 1 0^{17}$

No. of photons $= \frac{E}{( hc / λ )}$
$= \frac{9 \times 1 0 ^{- 3} \times 6.67 \times 1 0 ^{- 7}}{6.6 \times 1 0 ^{- 34} \times 3 \times 1 0 ^{8}}$
$= 3 \times 1 0^{16}$

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