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 second on the average at a target irradiated by this beam is

Step-by-step solution

Here =667 10⁻⁹ ~m , P =9 10⁻³ ~W aligned Power & = energy time & = n h c t & = N h c aligned where is number of photons emitted per sec. aligned N & = P hc & = 9 10⁻³ 667 10⁻⁹ 6.6 10⁻³⁴ 3 10^8 & =3 10¹⁶ / s aligned