The Dielectric Constant of Air (at sea level)

[chiques]

Does anyone have an idea of ‘how’ the dielectric constant of air is determined (calculated)? For example, how do pressure, humidity and temperature affect the published values on https://en.wikipedia.org/wiki/Dielectric_strength .

I would like to run some experiments which can adjust the DK of air by varying some of these environmental parameters.

 

[chuckey]

If you put DC on a capacitor, the positive plate drags electrons off the dielectric molecules on to its self. So if the temperature increases, the electrons "jiggle" more so some re-combine to their molecules.So the capacitance falls. If moisture is present then there will be little conducting paths withing the air, so again, more electrons return to where they came from. So the capacitance falls. If the pressure increases, then there are more molecules about, so I guess more electrons get dragged off, leading to an increase in capacitance.
Frank

 

[FvM]

You are asking about dielectric constant (permittivity) but quoting an article about dielectric strength (breakdown voltage). Do you understand the difference?

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The relative permittivity of air is very near to 1 (1.0005364 for dry, CO2 free air). The variations are respectively low and not easy to measure.

 

[kthackst]

This is a cool idea. Apparently the permittivity of air does not change much relative to barometric pressure, but changes in capacitance can be measured as a function of humidity and temperature: https://en.wikipedia.org/wiki/Relative_permittivity
This site also links to this particular thesis, which seems to describe the idea in detail: https://repository.tudelft.nl/islan...0d-4eb5-9f2e-b5b8e67af2e5?collection=research

I imagine, however, it took good deal of investigating to find a power and frequency regime where the permititvity of air would change enough that one could obtain useful measurements.