How much resistance does air provide.

[ICRS]

Like this wire with electric current ->----------------[ <-----1 metre-----> ]----------------

How much resistance with 1 metre of air provide. Assuming standard atmospheric ratio of gasses.

 

[Soundmanred]

Wut our a meeter?

 

[frostedflakes]

Not exactly what you were looking for, but according to first Google link I found, breakdown voltage of air is approximately 3kV/mm. I'd assume this is for dry air, though -- higher humidity may significantly decrease resistance and breakdown voltage.

 

[PlasmaBomb]

Originally posted by: frostedflakes
Not exactly what you were looking for, but according to first Google link I found, breakdown voltage of air is approximately 3kV/mm. I'd assume this is for dry air, though -- higher humidity may significantly decrease resistance and breakdown voltage.

So that would be 3 MV??

 

[91TTZ]

Originally posted by: PlasmaBomb

Originally posted by: frostedflakes
Not exactly what you were looking for, but according to first Google link I found, breakdown voltage of air is approximately 3kV/mm. I'd assume this is for dry air, though -- higher humidity may significantly decrease resistance and breakdown voltage.

So that would be 3 MV??

I think this question will be tougher to answer than that since we're going to be dealing with ionized air. For instance, the voltage require to bridge that gap will be much higher than is required to make a current flow once that spark is established.

Have you ever welded anything? You can get the stick pretty close without any spark forming, but once you strike it you can drag that arc pretty far away.

 

[BassBomb]

parody?

 

[BrownTown]

The resistance isn't the issue here, the breakdown voltage is what matters. The resistance of air will be VERY high, but at a point the voltage is high enough to ionize the air and then the resistance will be TINY.

 

[LordMorpheus]

Originally posted by: PlasmaBomb

Originally posted by: frostedflakes
Not exactly what you were looking for, but according to first Google link I found, breakdown voltage of air is approximately 3kV/mm. I'd assume this is for dry air, though -- higher humidity may significantly decrease resistance and breakdown voltage.

So that would be 3 MV??

3MV to start it, much less to maintain ... this is actually really bad because once you get your arc you'll probably wreck your power supply.

Look up some info on jacob's ladder.

two wires next to each other, verticle. Close at the bottom, far apart at the top (like a V).

the arc starts at the closest point, of course, at the bottom. The superheated plasma that is conducting the current rises in air, and the arc continues up to the top of the ladder, an area that was too far apart for it to start the arc due to the breakdown voltage of air, but once it's got the arc it can maintain it there.

it does, however, keep going up until the arc climbs off the ladder and dies, and then restarts at the bottom.


What you want to do would require immense power. I don't even think those giant diesel welders you see at construction sites could maintain a 1-meter arc. That's huge.

 

[ICRS]

Originally posted by: LordMorpheus

Originally posted by: PlasmaBomb

Originally posted by: frostedflakes
Not exactly what you were looking for, but according to first Google link I found, breakdown voltage of air is approximately 3kV/mm. I'd assume this is for dry air, though -- higher humidity may significantly decrease resistance and breakdown voltage.

So that would be 3 MV??

3MV to start it, much less to maintain ... this is actually really bad because once you get your arc you'll probably wreck your power supply.

Look up some info on jacob's ladder.

two wires next to each other, verticle. Close at the bottom, far apart at the top (like a V).

the arc starts at the closest point, of course, at the bottom. The superheated plasma that is conducting the current rises in air, and the arc continues up to the top of the ladder, an area that was too far apart for it to start the arc due to the breakdown voltage of air, but once it's got the arc it can maintain it there.

it does, however, keep going up until the arc climbs off the ladder and dies, and then restarts at the bottom.


What you want to do would require immense power. I don't even think those giant diesel welders you see at construction sites could maintain a 1-meter arc. That's huge.

So then lightning must have a lot of power to be able cross miles of air.

 

[BoomerD]

How many volts/amps are you needing to arc that distance?

As a crane operator, 10 feet is the minimum distance from 50kV lines, and I've seen electricity jump from high voltage lines to well-grounded cranes at only slightly less than that distance when the atmospheric conditions are just right. (high humidity, foggy, etc.)

 

[Born2bwire]

Air isn't resistive, it's capacitive.

 

[BrownTown]

Originally posted by: ICRS
So then lightning must have a lot of power to be able cross miles of air.

Well yes, lighting DOES have a lot of power, but also cosmic rays can also start the breakdown, so it doesn't have to reach the full breakdown voltage. A cosmic ray can come in and knock a bunch of electrons off some air molocules. The electrons are accelerated due to the electric field and then they hit into other atoms knocking off their electrons which creates an "avlanche" breakdown effect creating a conducting path to ground which then allows a huge amount of energy to be released creating the visible flash.

 

[Shadow Conception]

Wait what, I thought resistance was measured in ohms.

 

[Rubycon]

You need a lot of voltage to initiate breakdown as shown here.

You can get arcs very long without high voltage as long as the current is sufficient. An arc is hot and if there is sufficient current it can be dragged out many centimeters. (as in the case of a pole pig ballasted to 15kVA) Just remember that this is extremely dangerous because at these voltages lethal amounts of current WILL flow through your body and the outcome 99% of the time is electrocution.

 

[NikolaeVarius]

Originally posted by: ICRS

Originally posted by: LordMorpheus

Originally posted by: PlasmaBomb

Originally posted by: frostedflakes
Not exactly what you were looking for, but according to first Google link I found, breakdown voltage of air is approximately 3kV/mm. I'd assume this is for dry air, though -- higher humidity may significantly decrease resistance and breakdown voltage.

So that would be 3 MV??

3MV to start it, much less to maintain ... this is actually really bad because once you get your arc you'll probably wreck your power supply.

Look up some info on jacob's ladder.

two wires next to each other, verticle. Close at the bottom, far apart at the top (like a V).

the arc starts at the closest point, of course, at the bottom. The superheated plasma that is conducting the current rises in air, and the arc continues up to the top of the ladder, an area that was too far apart for it to start the arc due to the breakdown voltage of air, but once it's got the arc it can maintain it there.

it does, however, keep going up until the arc climbs off the ladder and dies, and then restarts at the bottom.


What you want to do would require immense power. I don't even think those giant diesel welders you see at construction sites could maintain a 1-meter arc. That's huge.

So then lightning must have a lot of power to be able cross miles of air.

Yes. Which is why saying that a car is safe from lightning as the rubber from the tire stops it from hitting the ground is retarded.

 

[Rubycon]

Motorcars are safe(er) because of the Faraday cage effect. Strikes will just jump around the tyre's sidewall to ground. Tyres are also poor insulators as the compounds contain carbon and steel reinforcing belts.

http://www.youtube.com/watch?v=i90gHhXYQBQ

Now a convertible or FRP/RIM (rooftop) would be another story! :Q

 

[TitanDiddly]

The dielectric breakdown voltage of air is highly dependent on humidity and a bucket of other factors, but the rule of thumb is about 20kV per inch.

 

[BrownTown]

Originally posted by: Shadow Conception
Wait what, I thought resistance was measured in ohms.

Resistance is measured in ohms. What people are talking about however is the fact that the resistance of a material isn't really a cosntant. At a high enough voltage there will be a "breakdown" where the airs resitance will drop MANY orders of magnitude, so just listing one value of resistance in ohms is misleading since at high electric fields the resistance won't be the same.