Yeah, talk about Einstein and Planck.
The idea of quanta was first hypothesised by Planck but only believed it was a mathematical trick to explain radiation curves of a black body. The dominance of the classical theory caused few scientists to take the idea seriously. Einstein, a prominent physicist at the time believed in the idea of the quantisation of light. He utilised Planck's idea to explain the photoelectric effect.
Einstein explained that:
1. Light existed in discrete packets called "photons".
2. Each photon carried energy where that energy was the minimum energy for a particular frequency.
3. Each material has a certain minimum amount of energy to induce the photoelectric effect - this is called the work function.
4. Energy transfer of a photon to an electron exhibits the all or nothing principle. If energy of a single photon is above the work function, its energy can be absorbed where excess energy becomes the electrons kinetic energy.
5. If the energy of a single photon is below the work function, no photoelectric effect will occur because energy is not enough to liberate a single electron.
6. The energy of a photon is proportional to its frequency such that E=hf.
Einstein's explanation demonstrated the physics behind the photoelectric effect. The photoelectric effect could not be explained by the classical theory because the presence of a threshold frequency before the photoelectric effect occurred could not be understood. Einstein's explanation clarified this lacking in the classical theory.
