An Etymological Dictionary of Astronomy and Astrophysics
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A device consisting of two electrodes separated by a small gap that is filled by a gas, usually air. A high → potential difference applied to the electrodes ionizes the gas and current flows across it for a brief time causing a spark across the gap. Spark gaps have a wide application. As spark plugs, they are used to ignite a mixture of fuel and air in the piston cylinders of an internal combustion engine. The electricity is provided by the battery and ignition coil, and the spark timing is controlled by the distributor. Spark gaps are also used as safety devices on equipment to prevent damage from voltage surges.

→ spark; → gap.