Electromagnetic radiation

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

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