Question

What is the energy of a single photon that has a wavelength of 420 nm? What is the energy of a mole of photons with this wavelength?

Answer 1

Wavelength = 420 nm = 420 x 10^-9 m

Energy of single photon = (h * c) /

where h = Planck's contant = 6.626 x 10^-34 J.s

c = speed of light = 3.0 x 10⁸ m/s

= wavelength = 420 x 10^-9 m

Substituting the values

Energy of single photon = (6.626 x 10^-34 J.s * 3.0 x 10⁸ m/s) / (420 x 10^-9 m)

Energy of single photon = 4.73 x 10^-19 J

Energy of one mole of photon = (Energy of single photon) * (Avagadro's number)

Energy of one mole of photon = (4.73 x 10^-19 J) * (6.022 x 10²³)

Energy of one mole of photon = 2.85 x 10⁵ J

Energy of one mole of photon = 2.85 x 10² kJ