| Type | Chemical and quantum phenomenon |
| Discovery | Early 20th century |
| Impact on | Solar energy • Solar power development |
| Discoverer | Max Planck |
| Related to | Quantum mechanics • Atomic physics |
| Application | Understanding electron and atom behavior • Development of quantum mechanics and atomic physics |
The photoelectric effect is a chemical and quantum phenomenon in which electrons are emitted from a material when it absorbs photons (particles of light). The effect was first discovered by the chemist Max Planck in 1911 as part of his work on colorimetry. Planck was studying the behavior of electrons when he was moved to investigate the possibility that light might exert a measurable force on them.
Planck was not the first to suspect that light could affect electrons in metals, but the idea was not taken seriously in scientific circles. Nevertheless, he persisted and discovered that low-energy (long-wavelength) light had the ability to eject electrons from a metal surface, provided the light was above a certain frequency threshold. The effect became known as the "Planck-Stark effect," after Planck and his assistant Johannes Stark.
Initially, the photoelectric effect was considered solely a chemical process. Planck and other chemists struggled to explain it alongside the established Lavoisier's Law and Dalton's Law, which dealt with the behavior of atoms and gases. Nevertheless, Planck's discovery sparked interest among physicists who saw in it the potential to explain quantum phenomena and the structure of the atom.
Early experiments using the photoelectric effect proved that atoms could absorb and emit energy in discrete packages or "quanta." This finding directly contradicted classical theories that electrons orbited the nucleus in continuous paths. It also helped establish the concept of particle-wave duality, which states that subatomic particles can also behave as waves.
In 1926, a young physicist named Erwin Schrodinger showed that the photoelectric effect could be used to explain electron orbital structure in atoms. This marked the birth of quantum mechanics as a coherent theory, which would in turn revolutionize physics and engender many of the key scientific advancements of the 20th century.
The photoelectric effect also gave rise to a new application of quantum mechanics: the photoelectric cell (also known as the "photocell" or "solar cell"). A photoelectric cell absorbs light and directly converts it into electricity. However, its adoption proceeded at a snail's pace for much of the 20th century. Renewable energy sources like solar power and wind power simply did not receive as much interest or investment as fossil fuels and nuclear power.
The lack of development around photoelectric cells impacted the growth of solar power and its potential applications for sustainability. While Planck's work in the early 20th century had pointed to the possibility of generating energy directly from sunlight, the limitation of technologies and lack of focus on renewable energy kept solar from becoming a cheap and viable source of electricity. It has only been in recent years that solar power has started to become competitive with fossil fuels.
In this alternate timeline, the photoelectric effect never attained the same prevalence or impact in scientific research and technological development. As a result, our understanding of quantum mechanics may have been limited, and the potential for solar power as a sustainable energy source may have been vastly underutilized.
