The Physics
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Dielectric Strength of Air

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Tipler, Paul A. College Physics. Worth, 1987: 467. "This phenomenon, which is called dielectric breakdown, occurs in air at an electric field strength of about Emax = 3 × 106 V/m." 3 × 106 V/m
Rigden, John S. Macmillan Encyclopedia of Physics. Simon & Schuster, 1996: 353. Air; Dielectric Constant, 1; Strength Es (kV/mm), 3 3 × 106 V/m
Yager, W. A. Digest on Literature on Dielectrics Volume X. Murray Hill, NJ: Bell Telephone Laboratories, 1947: 44-46. "Minimum sparking potentials in helium are 146, 161 and 187 volts" 146 V
161 V
187 V
Hodgman, Charles D. & Norbert A. Lange. Handbook of Chemistry and Physics 10th Edition. Cleveland, OH: Chemical Rubber Publishing Co, 1925: 547. "Spark length (cm), .10; Point electrodes, 3720; Ball electrodes, 1 cm diameter: Steady potential, 4560; Alternating potential, 4400" 3.7–4.5 × 106 V/m
Riley, Lewis A. Dielectrics. 1999-2000. "The dielectric strength of air is about 3 × 106 V/m" 3 × 106 V/m

Dielectric breakdown occurs when a charge buildup exceeds the electrical limit or dielectric strength of a material. The negatively charged electrons are pulled in one direction and the positively charged ions in the other. When electrons are removed from a nucleus, it becomes positively charged. When air molecules become ionized in a very high electric field, the air changes from an insulator to a conductor. Sparks occur because of the recombination of electrons and ions. Lightning occurs when there is a buildup of charge on the clouds and the ground It produces the electric field that exceeds the dielectric strength of air. Ionized air is a good conductor and provides a path where by charges can flow from clouds to ground.

The dielectric strength of air is approximately 3 kV/mm. Its exact value varies with the shape and size of the electrodes and increases with the pressure of the air.

Alice Hong -- 2000

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