How many photons are contained in a burst of yellow light 589nm from a sodium lamp that contains 609 kj of energy?

Answer 1

Given: 589 nm and Epulse 609 kJ

Find : # of photons

589 nm x m/109 = 5.89 x 10-7

E = 6.626 x 10-34 Js x 300 x 108m / 5.89 x 10-7 m = 3.3748 x 10-19 609 kJ x J/0.001 x 1 photon/3.3748 x 10-19 = 1.80 x 1024 photons

Answer 2

The question lists two photons of radiation with the same wavelength.

The energy of a photon is given as [ E = (h) x (frequency) ] = (h) x (c/wavelength).
So all photons with the same wavelength (and frequency) have the same energy.

If their wavelengths were different, then their energies would differ by a factor equal to
the reciprocal of their wavelengths, i.e. proportional to their frequency.