Photoelectric Effect

In the Photoelectric Effect Gizmo, students learn about a very interesting phenomenon. When you shine light on certain metals, the energy from the light can liberate electrons from the surface of the metal. The number and energy of the emitted electrons depends on the frequency and intensity of the light.

While the photoelectric effect may seem like a fairly obscure topic, it occupies an important place in the history of physics. Conventional wave theory would predict that the kinetic energy of the emitted electrons would be proportional to the intensity of the light. Instead, increasing light intensity had no effect on the energy of electrons, only on the number of emitted electrons. In 1905, Albert Einstein realized that this evidence supported a new theory that light energy was transmitted in individual packets, or quanta. This helped establish quantum theory and it was this work, rather than relativity, that earned Einstein his Nobel Prize in physics in 1921.