In 1905, Einstein postulated the proportionality between the frequency f {\displaystyle f} of a photon and its energy E {\displaystyle E} , E = h f {\displaystyle E=hf} , and in 1916 the corresponding relation between photon's momentum p {\displaystyle p} and wavelength λ {\displaystyle \lambda } , λ = h p {\displaystyle \lambda ={\dfrac {h}{p}}} , where h {\displaystyle h} is the Planck constant.
Pada tahun 1905, Einstein mempostulatkan hubungan kesebandingan antara frekuensi f {\displaystyle f} dari suatu foton dan energinya E {\displaystyle E} , E = h f {\displaystyle E=hf} , dan di tahun 1916 hubungan yang terkait antara momentum p {\displaystyle p} dan panjang gelombang λ {\displaystyle \lambda } foton, λ = h p {\displaystyle \lambda ={\dfrac {h}{p}}} , di mana h {\displaystyle h} adalah konstanta Planck.