Photoelectric Effect



Experiments show that electrons are ejected from the surface of certain metals (like Cs, K and Rb) when they are exposed to light to appropriate frequency. This phenomenon is known as photoelectric electric.



    According to the wave theory of light, both the number of electrons ejected and their energies should depend on the intensity of the incident light. In practice, it is found that while the number of electrons ejected does depend on the intensity of the incident light, their energies do not. Einstein was able to explain the photoelectric effect by making the most extraordinary assumption. He suggested that light consists of streams of particles called photons which move with the speed of light. Using Planck’s quantum theory of radiation as a starting point. Einstein deduced that each photon must possess energy E, given E = hv where v is the frequency of light.



    Shooting a beam of light onto a metal surface can, therefore, be viewed as shooting a beam of particles – the photons. When a photon strikes an electron in the atom of the metal with sufficient energy, the electron may be knocked out of the atom. The more energetic the photon is, the more energy it transfers to the electron and the greater the energy of the rejected electron. A more intense beam of light consists of a large number of photons, consequently the number of electrons ejected is also larger as compared to an experiment in which a beam of weaker intensity of light is employed.