Question

A monochromatic source ,emitting light of wavelength 600 nm,has a power output of 66W .calcul;ate the number of photons emitted in 2 minutes?

Answer 1

Wavelength, λ = 600 nm = 6 × 10^-7 m

Power of the source is, P = 66 W

Now, energy of each photon is, E = hc/λ = (6.626 × 10^-34)(3 × 10⁸)/(6 × 10^-7) = 3.313 × 10^-19 J

Suppose, ‘n’ is the number of photons emitted per second so that the energy per second is 66 W

So, nE = 66

=> n = 66/(3.313 × 10^-19) = 1.99 × 10²⁰ photons/s

So, photons emitted in 2 minutes is = n × 2 × 60 = 2.388 × 10²² photons