Physics > modern-physics > Dual Nature Of Radiation And Matter

**Case Study: Photoelectric Effect** Einstein explained the photoelectric effect on the basis of Planck''s quantum theory. Light travels as discrete packets or photons of energy $h\nu$. The number of photons incident per unit time per unit area (intensity) determines the magnitude of the photoelectric current. When a photon is incident on a metal surface, it transfers all its energy $h\nu$ to a free electron. A portion of this energy is used to overcome the surface barrier (known as the work function, $\phi_0$), and the remaining energy appears as the maximum kinetic energy ($K_{max}$) of the emitted electron. This relationship is defined by Einstein''s photoelectric equation: $$K_{max} = h\nu - \phi_0$$