Einstein proposed a new picture of electromagnetic radiation to explain the photoelectric effect. Photoelectric emission does not take place by continuous absorption of energy from incident radiation. Radiation energy is made up of special units called quanta of the energy of radiation. Each quantum has an energy h, if this energy exceeds the minimum energy to emit electron then the electron is emitted with maximum kinetic energy.
Kmax = h – φ0
Planck’s constant is h = 6.62 × 10−34 joule-sec.
This equation is known as Einstein’s photoelectric equation.