The Richardson-Dushman Equation 
It explains thermionic emission. When you heat a metal surface to a high temperature, some of its electrons gain enough energy to escape into the vacuum around it. The hotter the metal gets, the more electrons are released, and this happens very quickly once the temperature reaches a certain point. Different metals require different amounts of heat because they hold onto their electrons with varying strength. This process was used in old vacuum tubes, TV screens, and electron microscopes to create streams of electrons that power electronic devices.
It explains thermionic emission. When you heat a metal surface to a high temperature, some of its electrons gain enough energy to escape into the vacuum around it. The hotter the metal gets, the more electrons are released, and this happens very quickly once the temperature reaches a certain point. Different metals require different amounts of heat because they hold onto their electrons with varying strength. This process was used in old vacuum tubes, TV screens, and electron microscopes to create streams of electrons that power electronic devices.