Electromagnetic radiation can be understood as particles of energy called photons or quanta
Each photon (or quantum) has an energy E:
E = hf
- E energy photon in J or eV ( 1 eV = 1.6 x 10-19 J)
- h Planck’s constant h = 6.626 x 10-34 Js
- f frequency in Hz
- c speed of light (cvac= 3.00 x 108 ms-1)
- λ wavelength in m
The frequency f and the wavelength λ are related to the speed through the relation
c = fλ
Example
Find the energy of photons of yellow light (λ = 580 nm)
c = fλ f = c/λ = (3.00 x 108) /( 580 x 10-9) = 5.172 x 1014 Hz
E = hf = (6.626 x 10-34)( 5.172 x 1014) = 3.238 x 10-19 J =( 3.238 x 10-19)/(1.6 x 10-19) = 2.02 eV