Question

What is the number of photons of light with a wavelength of 4000 pm that provide 1 J of energy?

Answer 1

Energy (E) of a photon = hν

Energy (E_n) of ‘n’ photons = nhν

Where,

λ = wavelength of light = 4000 pm = 4000 ×10^–12 m

c = velocity of light in vacuum = 3 × 10⁸ m/s

h = Planck’s constant = 6.626 × 10^–34 Js

Substituting the values in the given expression of n:

Hence, the number of photons with a wavelength of 4000 pm and energy of 1 J are 2.012 × 10¹⁶.