# Electric vs magnetic field

1. Aug 12, 2013

### Crazymechanic

Now before I ask the question I must say i understand that geometry and also density and volume takes into account in all of this deciding but in overall I am sure you could give me an answer.
So say I have a tube or a sphere or some other geometry object in a normal everyday size like say 2 cubic metres of volume ad I have some hydrogen or other gas (ionized) in it , now say I would like to compress it which compressing method would be able to compress the gas stronger?

Now you might be wondering what a stupid kinda question this is but no I am interested in this as from a theoretical standpoint , the thing is I don't want to hear some absolute theoretical possible compression ratios with both magnetic or electric field as I know that in the universe in large stars and neutron stars the magnetic field can be abnormaly extremely powerful , but here on earth in lab or industrial applications taking limited power supplies etc etc into account by which method we could compress a (ionized) gas more with a magnetic field requiring lots of current hence power consumption or by a very very strong high voltage electric field say?

Last edited: Aug 13, 2013
2. Aug 12, 2013

### Drakkith

Staff Emeritus
You can't compress a gas/plasma using only an electric field.

3. Aug 12, 2013

### nsaspook

I wouldn't make a blanket statement, Einzel lens and electric quadrupoles can longitudinally focus/compress a charged (ion) beam.

4. Aug 12, 2013

### Drakkith

Staff Emeritus
Sure, but that's a beam. I assumed the OP was referring to taking a volume of gas and simply compressing it, not turning it into a beam of ions first.

5. Aug 13, 2013

### Crazymechanic

Ok excuse me , again working late forgot to say that i was thinking about a volume of ionized gas , say hydrogen.Ofcourse it would be impossible to compress both ions and electrons when they are together with an electric field.
So now that I have corrected my post i hope you can carry on with some answers, Thanks.

6. Aug 13, 2013

### Drakkith

Staff Emeritus
Imagine the "charged hollow sphere" example. Inside the sphere the potential is the same everywhere, so no force will be exerted on any of the particles, no matter their charge.

7. Aug 13, 2013

### cragar

I wonder if you could do it in a tube of gas. What if you had a strong E field pointing down the tube.
The E field would induce an Electric dipole in the molecule an attract it to one end.

Last edited: Aug 13, 2013
8. Aug 13, 2013

### Crazymechanic

Yes drakkith I know that inside a conducting sphere or tube there is no E field as all the charge resides on the outer surface , well then take the pressure effect as the gas would be between two conducting plates or around a conducting sphere which is inside another sphere.
It's not so much the practical physical design than rather the theory that I am interested this time.
There are ways in which an E field can be used to put or exert a pressure on a gas and I wanted to know in which way the pressure could be made stronger by human means and ways of technology , using an electric or magnetic field? I hope you understand what I' trying to get here :)

9. Aug 13, 2013

### cragar

10. Aug 13, 2013

### Crazymechanic

Ok that's about the magnetic field , how about the electric one , well i once remember reading up on an article about very short distance pulse mode magnetic fields getting up to extreme levels.

Well honestly speaking I was hoping for someone to give me some numbers in like the force (theoretical) that can be exerted on a ionized gas considering both fields.It got me wondering because a magnetic field can be strong but then again to create one you basically need thick wires , good conductors , then cool those down to some low temperatures to make them superconducting and still you need to run alot of amps through them to make the field strong , now with the electric field there are some advantages like no need for cooling something , small power consumption etc.
Ok let me ask it like this , if had a given volume, density of gas and the aim would be to compress it as much as possible which way could I do it better , given the power supply is limited etc.

Last edited: Aug 13, 2013
11. Aug 13, 2013

### Drakkith

Staff Emeritus
No, I have absolutely no idea what you're trying to get.
You simply can't use an electric field to put pressure on a static volume of gas as far as I know.

What pressure effect? Between two plates the gas would just be pushed out the sides, not compressed, wouldn't it? As for a sphere inside a sphere, if the voltage was the same then nothing would happen. And if it wasn't, well then you'd just push the ionized gas up against the other sphere and have a big mess as the ions interact with the metal. (And that's if anything would happen at all)