Townsend criterion

The Townsend criterion is a principle in physics that helps determine when a gas becomes conductive—essentially when it can conduct electricity. It assesses the conditions under which free electrons can move and cause an electric current in a gas. When the electric field strength reaches a certain level, it can accelerate these electrons enough to create ionization, resulting in a chain reaction that allows electricity to flow. Understanding this concept is crucial in fields like plasma physics and atmospheric science, as it explains phenomena such as lightning and the behavior of gases under electric fields.