A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the potential difference between the conductors exceeds the breakdown voltage of the gas within the gap, a spark forms, ionizing the gas and drastically reducing its electrical resistance. An electric current then flows until the path of ionized gas is broken or the current reduces below a minimum value called the "holding current". This usually happens when the voltage drops, but in some cases occurs when the heated gas rises, stretching out and then breaking the filament of ionized gas. Usually, the action of ionizing the gas is violent and disruptive, often leading to sound, light, and heat.
The switch contacts on a multimeter acting as a PCB spark gap.
A photo of a handgun firing, taken with an air-gap flash. The photo was taken in a darkened room with the camera's shutter open, and the flash was triggered by the sound of the shot using a microphone.
Spark gap tube
An electric spark is an abrupt electrical discharge that occurs when a sufficiently high electric field creates an ionized, electrically conductive channel through a normally-insulating medium, often air or other gases or gas mixtures. Michael Faraday described this phenomenon as "the beautiful flash of light attending the discharge of common electricity".
A spark on a spark plug
Lightning is a natural example of an electric spark.
Benjamin Franklin drawing an electric spark to his finger from a key suspended from a kite string.
Gas stove burner - the electric spark flame igniter is shown at the left.