Why do Parallel Currents Attract?

[krab]

I am in the understanding that the magnetic field is just a relativitic effect

...

This is your magnetic force... its just a lot easier to use the magnetic force equations that were already hashed out before relativity than apply lorentz contractions to electric fields all the time and this is prolly why it is allways tought as a separate force.

...

Good post, axaware.
I'm always a little suspicious of statements of the type "such-and-such effect is just a consequence of such-and-such", as if an alternative description makes everything simpler. In some situations it does, in others it does not. So, looking at a beam of particles traveling together in vacuum, contemplating the fact that there is a magnetic field in the lab frame but none in the particles' rest frame, can teach one a lot about relativity. OTOH, forces between neutral, current-carrying wires are not more easily described by appealing to relativty.

 

[Epsilon Pi]

Hi Vince,

This is an explanation, from the point of view of the basic unit system concept, not a why things are in a such a way.
In fact the magnetic field is clearly a dual entity because of its two inherent polarities and as such we must represent it by a complex entity such as the BUS, which has both kinds of parities:
- that one that has to do with space that has consequently both signs: positive and negative, as it were, attractive and repulsive,
- but it also has even parity, the one that is associated with sort of non relativistic effect, it remains the same in spite of change; is not this a reason why it was precisely the magnetic field in weak interactions the medium to break symmetry?

When the sense of rotation according to the right-hand rule is the same the forces are attractive, but it is not the same when that sense is inverse, as is the case. We must take into account that with that rotation is associated a frequency, so in one case we have resonance, but not in the other.
Regards
EP
PD: or in one case the prevailing one is the magnetic field, and on the other the electric field or charge of the electrons that repel each other as the magnetic field is cancelled?

I've read that when currents in two parallel wires are going in the same direction, they attract each other. The same text said that when the currents are going in opposite directions, the two wires repel each other.
Why does this happen? Is there a different behavior for AC and DC currents?

 

[Metallicbeing]

hi,

I am in the understanding that the magnetic field is just a relativitic effect

Simplified picture...
you take two really long parallel wires 1 and 2. These wires appear neutral.

Okay, remember that in relativity that things moving relative to one another will see each other being shorter from space contractation... I am just going to ignore time aspect.

Anyway we run an electron current through both wires same magnitude and direction. (only electrons are moving)

So the moving electrons in wire 1 sees the electrons in wire 2 as stationary (as they are both moving same speed+direction) so they would feel the normal electric repulsive force. BUT now the moving electrons in wire 1 sees the protons in wire 2 as moving and so sees the protons in wire 2 as space contracted resulting in wire 1 electrons seeing a higher proton density than electron density in wire 2 so the electric attractive force to the protons is greater than the repulsive electric force from the eletrons. SO wire 1 is attracted to wire 2 because the moving electrons in wire 1 see wire 2 as being positivily charged from the space contraction.

Now the stationary protons in wire 1 sees similar effects in wire 2 but this time the stationary protons see stationary protons so same electric repulsive force here. BUT this time the stationary protons in wire 1 sees moving electrons in wire 2 these moving electrons in wire 2 appear space contracted to wire 1 protons perspective resulting in wire 1 protons seeing a higher electron density than proton density in wire 2 so the electric attractive force to the electrons in wire 2 is greater than the repulsive force from the protons in wire 2. SO wire 1 is attracted to wire 2 because the protons in wire 1 see wire 2 as being negativily charged from the space contraction.

So looking at the electrons perspective in wire 1 it is attracted to wire 2
looking at the protons perspective in wire 1 it is attracted to wire 2
So wire 1 is attracted to wire 2

Same anaylsis can be done for wire 2 looking at wire 1 and you will find that wire 2 is attracted to wire 1

although the electrons are moving really slowly this force is really small... but there are SO MANY electrons and protons in the material it makes the effect really significant.

This is your magnetic force... its just a lot easier to use the magnetic force equations that were already hashed out before relativity than apply lorentz contractions to electric fields all the time and this is prolly why it is allways tought as a separate force.

on the flipside in http://www.iop.org/EJ/abstract/0143-0807/17/4/006 indicates that its just as reasonable to say that the electric field is the relativistic effect... but then again maybe not...
http://www.iop.org/EJ/abstract/0143-0807/18/2/013

I put my dime with relativity on this one.

sorry for any crappy spelling mistakes etc...

Axawire,

Your explanation was very good. I'm sure you could have said the same thing with an equation, but I'm glad that you resisted. There are many here who miss out because some only "speak" with math. I've tried to speak in layman terms to others who want to learn, only to be bashed at almost every turn for not speaking in the "proper tongue". My hat's off to you.

 

[Chronos]

Apologies. We only speak in 'math' because that is the only language of science that is known. Propose a better 'language' and go collect your nobel. In other words, I think you have mastered bull-speak... Just like the Andrew Grey. I have not even totally figured out the simplest dq equations of anything in the universe. Show me yours.

 

[what_are_electrons]

Apologies, we only speak in 'math' because that is the only language of science that is known. Propose a better 'language' and go collect your nobel.

How 'bout drawings/pictures plus math to give a 1,000 and 1 words/descriptions? That way, us How To Dummies, can keep pace as best we can despite our illiteracy. That fair?

 

[Chronos]

I would say you can't picture it.

 

[Math Is Hard]

I would say you can't picture it.

I agree with Chronos. For instance, how would you draw a picture of a five-dimensional object? Math allows us to describe things even where our visualizations fail us.

 

[Chronos]

apologies, you can't even describe it in 3 dimensions.

 

[Chronos]

What math are you supporting?

 

[Chronos]

Duh, I have no math! Just totally wrong ideas!

 

[Math Is Hard]

apologies, you can't even describe it in 3 dimensions.

You got to 'splain that to me, Lucy. If I start another thread will you give me more details? I don't want to derail here.
Seriously, I want to understand this, though.

 

[Chronos]

quantum spin is a way to differentiate all the difficulties of telling them apart. i don't think they actually 'spin' in the same way we would dance.

 

[Epsilon Pi]

A fivefold structure of reality?

Yes, it has no physical meaning to extend the concept of dimension to five; why don't we talk better about determining the state of a system in the complex plane, where both time and space are included, having then sort of fivefold structure of reality?
Regards
EP

I agree with Chronos. For instance, how would you draw a picture of a five-dimensional object? Math allows us to describe things even where our visualizations fail us.

 

[Locrian]

How 'bout drawings/pictures plus math to give a 1,000 and 1 words/descriptions? That way, us How To Dummies, can keep pace as best we can despite our illiteracy. That fair?

It won't help anyone keep pace. If someone doesn't know math, they can know no physics, pictures or not. Luckily though, this is also a math help board. Anyone who is behind on their math can get started learning and post questions in the appropriate sections...

 

[Metallicbeing]

Apologies. We only speak in 'math' because that is the only language of science that is known. Propose a better 'language' and go collect your nobel. In other words, I think you have mastered bull-speak... Just like the Andrew Grey. I have not even totally figured out the simplest dq equations of anything in the universe. Show me yours.

Chronos,

Anyone who has said anything in only words in this forum concerning any kind of theory always results in someone saying they're speaking "bull-speak". Show me otherwise.

I agree that math is nearly the only way to pose a theory properly. What I'm talking about is helping the people out there that may not have the education required to understand the formulas put forth, but would like to at least get some kind of grip on the concept these formulas represent. Obviously, you might use simplistic terms for someone who is not yet at an advanced level of understanding.

Or, are you saying that this forum is your own club and others of "limited" education shouldn't even be here. Everyone should be invited to learn as much as they can about science. There are too many people out there who know very little or nothing of science. Don't shut them out.

 

[Integral]

This thread has gotten way off topic, Clearly it has ended any useful purpose.