Minimum arc voltage of air was: Definitions of High Voltage

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi Boris,

Tesla list wrote:

>
> Interesting is the fact that bellow 300-400 V in a
> very narrow gap there is still no gas discharge before
> metal to metal touch (standard atm. conditions).

Yes, it is interesting. North states that 340 is the "absolute minimum"
(in air), therefore, anything below this value should not arc a gap
regardless of eletrode size, shape, gap distance, or barometric
pressure. He goes on to say that breakdown voltage decreases as pressure
decreases until the 340V minimum is reached, due to the fact that as the
melocular density of air is reduced, there is greater likelihood that a
free ion can traverse the space between electrodes without running into
something. But (here's the thing), as pressure is further reduced, the
required voltage for breakdown increases once again because a more
limited number of air molecules make ionization more difficult. So, we
have a dip and it's value is 340V. Thus, it's the physical makeup of air
and pressure that give us this minimum voltage.

Take care,
Bart