Stories We Like: A Guide to the Comma
in physics, a sudden increase in the flow of an electrical current through a nonconducting or semiconducting solid when a sufficiently strong electrical force is applied. The ability of most nonmetallic solids to carry an ordinary electrical current is limited by the scarcity of electrons free to move in the presence of an externally applied electric field. A sufficiently strong electrical force can break free a large number of electrons from the atoms that form the structure of the solid so that a large current can flow through the material. This avalanche effect is responsible for the phenomenon of breakdown in insulators and in semiconductors, where it is called the Zener effect. Because avalanche requires a specific electrical force for each type of substance, it can be used for precise control of voltages in electrical circuits, as in a device called the Zener diode.