The phenomenon that demonstrated the particle-like behavior of light, leading to the development of quantum mechanics, is known as the __________.

The phenomenon that demonstrated the particle-like behavior of light, leading to the development of quantum mechanics, is known as the photoelectric effect. In this experiment, light striking a metal surface ejects electrons, and the amount of energy depends on the light’s frequency, not its intensity. This observation could only be explained if light came in discrete packets, or photons, each carrying energy proportional to its frequency. The result forced scientists to rethink light and matter, sparking the birth of quantum theory. For example, shining ultraviolet light on a metal surface releases electrons only when the light’s frequency exceeds a certain threshold, regardless of how bright the light is.