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Paschen's law[′päsh·ənz ‚lȯ]
a law stating that the sparking potential of a gas between two plate electrodes in a uniform electric field is a constant and is characteristic of the gas for identical values of pd, where p is the pressure of the gas and d is the distance between the electrodes. The law was formulated by F. Paschen in 1889.
Paschen’s law is a special case of a similarity law for gas discharges: the phenomena in a discharge proceed identically if two conditions are satisfied: (1) the product of the gas pressure and the electrode separation remains constant, and (2) the configuration of the electrode gap remains geometrically similar to the original configuration. Paschen’s law is approximate: the smaller p and d, the more accurately the law holds in experiments.