Question

What is number of photons of light with a wavelength of 400 pm that provide 1 j of energy?

Answer 1

Where,λ = wavelength of light = 400 pm = 400×10–12 m = 4x 10-8m
c = velocity of light in vacuum = 3 × 108 m/s
h = Planck’s constant = 6.626 × 10–34 Js
thefore the energy of photon (E)
= 6.626 × 10–34 Js X 3 × 108 m/s / 4x 10-9 m = 4.965 x 10-16 J
Now 4.965 x 10-16 J is the energy of = 1 photon
Therefore 1 J will be the energy of = 1/4.965 x 10-16 J = 2.014 x 1015 photons