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 = hc/λ

Where,λ = wavelength of light = 4000 pm = 4000 x 10^-12 m = 4 x 10^-9 m  

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

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

therefore the energy of photon (E)  = 6.626 × 10^-34 Js X 3 x 10⁸ m/s / 4 x 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