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discharging arc - voltage drop
xshadow:
Hi.
Studying discharging(electric) arc I don't undesrtand some phrases :
" when ionization energy of plasm constituents is higher the arc voltage drop increases"
" arc has much more electron density (current) than glow discharge and so the voltage is smaller"
Remember some physics formulas : V= IR
So if the curreint is higher (like in arc), the voltage also should be higher!! I'm missing something...mhh ???
Don't undesrtand...
Borek:
--- Quote from: xshadow on October 30, 2021, 02:24:48 PM ---Remember some physics formulas : V= IR
So if the curreint is higher (like in arc), the voltage also should be higher!!
--- End quote ---
Assuming constant R - which is not true in arc discharges.
xshadow:
--- Quote from: Borek on October 30, 2021, 04:48:30 PM ---
--- Quote from: xshadow on October 30, 2021, 02:24:48 PM ---Remember some physics formulas : V= IR
So if the curreint is higher (like in arc), the voltage also should be higher!!
--- End quote ---
Assuming constant R - which is not true in arc discharges.
--- End quote ---
why is R not constant?
R what is it?
The resistance of the dielctric/gas pahse?
I could think that a gas-phase (between the two electrodes) with more ions should conduct much easier ....is it correct?
thanks
Borek:
--- Quote from: xshadow on October 30, 2021, 04:59:20 PM ---why is R not constant?
--- End quote ---
--- Quote ---I could think that a gas-phase (between the two electrodes) with more ions should conduct much easier ....is it correct?
--- End quote ---
In terms of Ohm's law: the more the ions the lower the resistance. But: higher current means more heating, more collisions, and more ions, so the resistance changes during arcing.
xshadow:
--- Quote from: Borek on October 31, 2021, 03:43:16 AM ---
--- Quote from: xshadow on October 30, 2021, 04:59:20 PM ---why is R not constant?
--- End quote ---
--- Quote ---I could think that a gas-phase (between the two electrodes) with more ions should conduct much easier ....is it correct?
--- End quote ---
In terms of Ohm's law: the more the ions the lower the resistance. But: higher current means more heating, more collisions, and more ions, so the resistance changes during arcing.
--- End quote ---
Thanks Borek : )
Because I've read that:
in Glow discharge we have high voltage and low current
in electric arc we have instead low voltage and high current
So the low voltage in electric arc is due to the high-ionized gas in the medium (plasma) (the arc works at atmosferic pressure) --> low resistenze R --> it's required only a low voltage applied to electrode in order to get an high current
WHile I know that in glow discharge we have low current (due to few ionized species in the "medium" cause low gas pressure) but high applied voltage ...because we have few charge carriers (low pressure than arc)
Is it correct?
thanks :)
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