How to calculate the energy of light?

Question

Calculate the energy, in joules per photon, of the red line, 6573 Å, in the discharge spectrum of atomic calcium.

Answer 1

E = hv    where h is plancks constant and v is frequency and E is energy

6573 angstroms = 6.573 e-7 m = wavelength (λ)

First we must use: v = c/λ   where c is the speed of light

v = (3.00 e8 m/s)/(6.573 e-7 m) = 4.564e14/s

E = (6.63 e-34 J x s)(4.564 e14/s) = 3.026 e-19 J