How does Planck's constant relate photon energy to light frequency?

In the context of the photoelectric effect, Planck’s constant ($h$) serves as the fundamental proportionality factor that links the energy ($E$) of an individual photon to the frequency ($\nu$ or $f$) of the associated electromagnetic radiation. This relationship is expressed by the equation:

$$E=h\nu$$

Max Planck introduced this constant in 1900 to describe how radiation is emitted and absorbed in discrete packets, or quanta. Albert Einstein later applied this concept to the photoelectric effect, proposing that light itself consists of these energy quanta.123

Because the energy of a photon is directly proportional to its frequency, light with a higher frequency carries more energy per photon. This explains why the photoelectric effect depends on the frequency of the incident light rather than its intensity; only photons with a frequency high enough to meet the work function of a material can successfully liberate an electron.342