The formula we can use here is the Plancks equation:
E = h c / ʎ
where h is Plancks constant = 6.626 × 10-34 m2 kg / s, c
is speed of light = 3 x 10^8 m/s and ʎ is wavelength = 656.1 x 10^-9 m
Therefore E is:
E = (6.626 × 10-34 m2 kg / s)
* (3 x 10^8 m/s) / 656.1 x 10^-9 m
E = 3.03 x 10^-19 J
