Question

How many photons of light with a wavelength of 4000 pm are necessary to provide 1 j of energy?

Answer 1

energy of one photon = hc/λ

substituting the values of h = 6.626 * 10^-34 and c = 3 * 10^8 and λ = 4 * 10^-9

we get energy of one photon = 5 * 10^-17 joule

then 1 joule contains 1/(5 * 10^-17) photons = 2 * 10^16 photons