Question

Give Einstein's explanation of the photoelectric effect.

Answer 1

In 1900, Max Planck proposed the quantum theory to explain the blackbody spectrum. According to his hypothesis, the electromagnetic radiation that the body emits is made up of discrete concentrated bundles of energy, each of which is equal to hν, where h is the radiation's frequency and h is a universal constant that is now known as Planck's constant. According to Einstein's theory from 1905, these energy quanta later known as light quanta or photons interact with matter in a manner akin to that of particles. An electron in an atom absorbs all of the photon energy (hν) in a single collision or none at all when a photon collides with it.

The electron uses this energy in three ways: To break free from the atom, to go over the surface's potential energy barrier and break free from the metal, and to keep the remaining portion as its kinetic energy. In the first two stages, different electrons require different energy. Some electrons exit the metal with the greatest amount of kinetic energy because they use the least amount of energy during the two processes. The photoelectric work function (∅₀) of a metal is the lowest energy needed to liberate an electron from it in the form of electromagnetic radiation. Therefore, for the photoelectrons that were most energetic at the time of emission,

maximum kinetic energy of the electron = photon energy − photoelectric work function

∴ `1/2 mv_(max)^2` = hν − ∅₀

∴ `hν = ∅_0 + 1/2 mv_(max)^2`

The above equation is called Einstein’s photoelectric equation.

As concentrated bundles of energy rather than energy dispersed along a wavefront of the Huygens type, light interacts with matter. An electron can absorb a photon's energy in a single collision, even in weakly irradiated environments. On the other hand, because there are fewer incident photons in low light, there is less probability of such absorption, which lowers the photoelectric current. Nevertheless, the instant a photon is absorbed, a photoelectron is released.