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the general name for various types of physical processes that bring about an abrupt rise in electric current through a medium that is ordinarily nonconductive or only weakly conductive.
(1) Electrical breakdown in a vacuum is due to the formation of a conducting path by the particles of the electrode materials that are emitted as a result of secondary electron emission and ion emission (for the most part electron-ion emission). Particles of the residual gases, together with the electrons that are always emitted to some extent by electrodes into a surrounding vacuum, serve as the initiatory particles that accelerate in the electric field, bombard the electrodes, and begin the secondary emission. In very strong fields, tunnel emission (autoelectronic emission or autoionization) can play an important part in this type of electrical breakdown.
(2) Electrical breakdown in a gas-filled space is the initial stage of electrical discharge in the gas (seeSPARK DISCHARGE).
(3) For electrical breakdown in solid and liquid dielectrics and semiconductors, seeDIELECTRICS; SEMICONDUCTORS; and .