Question: Dielectric breakdown of air

[emzz]

Is there any specific object/equipment that you can use to measure the dielectric breakdown of air?

Or if there's no such equipment, is there any way to fix together some lab apparatus to construct something which can do so?

[YT2095]

2 plates X distance apart, a variable voltage HT generator wired to these plates, and a meter inline with one of the leads, you`ll get a needle kick as the air breaks down.

 

you have to remember though, this is only the DC breakdown, electricity at frequency will alter the breakdown voltage levels.

[emzz]

Oh ok. Could u explain further how it works?

I thought of using two plates but i wasn't sure whether it would work.

 

Thanks a lot!

[YT2095]

forget that it`s Air, just consider it a Dielectric.

and then treat the whole thing as it were a Capacitor, perform the same test you would do also.

 

Air is no different to any other material, in fact the early capacitors were Air gap types

[swansont]

You can also see this in a Geiger tube, at the breakdown voltage.

[YT2095]

Good point, these tubes are similar to Leyden jars (a capacitor) except they are much smaller and usually have a Halogen inside under low pressure.

 

a very high voltage several 100 volts is put across these elements, and a particle will enter and leave an ionised trail that conducts a little and it will crash the PD for a sec.

 

I`m also fairly sure you can get tables of Dielectric constants in most physics data books, even the Chemist bible the CRC handbook

[emzz]

Oh alright. Thanks a lot!

 

I'll check out some sites about dielectrics then. Not very well versed in these things.

[YT2095]

some of the tesla coil sites have pretty good links with tables for that sort of thing too.

 

hit any probs, just ask some more

[Fuzzwood]

Well to keep it very simple: top plate = cloud, bottom = ground. And you form a kind of lab-scale lightning by piling up electrons in the cloud plate. At one point it sparks.

[emzz]

Would something like this work?

(Sorry, not a very good artist)

 

Someone suggested that I try setting up a circuit like that

[YT2095]

skip the LED, it`s shorted out anyway in your diag.

the meter across the plates to read the voltage yes, and you`ll need another meter in line (in series) with one of the wires too.

[emzz]

Whoops. Didn't realise that I shorted out the LED.

 

Do you mean i put an ammeter in like this?

 

 

Thx

[YT2095]

yup, although a nice sensitive one would be good, as the breakdown isn`t actually a Sudden as it seems, there is a point when there is partial conduction, and then *CRACK* you get a spark. might be a good idea to use a resistor as soon as the power comes out the HT gen, when it arcs, it will act as a dead short and may damage the kit.