Explain the photoelectric effect and cite sources in the reply.
The photoelectric effect is a phenomenon where electrons are emitted from a material when it is exposed to light or other forms of electromagnetic radiation. The effect occurs because the photons in the light transfer their energy to the electrons, causing them to be released from the material. This effect has important applications in fields such as solar cells, photodiodes, and photography. The photoelectric effect was first observed by Heinrich Hertz in 1887 and later explained by Albert Einstein in 1905. This explanation earned him the Nobel Prize in Physics in 1921.

Sources for this information include the Nobel Prize website (https://www.nobelprize.org/prizes/physics/1921/einstein/facts/) and the HyperPhysics website (http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/photoelec.html)