Electric current makes magnetic field, why?

[alpha2cen]

Every one knows well electric current makes magnetic field.

Then, why does electric current make magnetic field?

[D H]

In classical electrodynamics, the answer is in Maxwell's equations, particularly the fourth one, the Maxwell–Ampère equation. Here's a reference on Maxwell's equations: http://galileoandeinstein.physics.virginia.edu/more_stuff/Maxwell_Eq.html

 

In special relativity, the answer also lies in Maxwell's equations, this time written in a manifestly covariant form. Magnetic fields and electric fields are observer-dependent manifestations of the same phenomenon.

 

I'll leave the QED (quantum electrodynamics) explanation up to our quantum mechanics specialists.

[swansont]

The short version of what D H linked to is that a magnetic field is what an electric field looks like when something is moving. What fields you see depend on what frame of reference you are in.

[alpha2cen]

Maxwell equations are relationships between electric current and magnetism.

Are there more primary cause of magnetic field generation?

Why does electric current through a conductor make magnetic field?

Are there any property against the electric current in a vacuum?

Edited January 31, 2011 by alpha2cen

[lemur]

Is there any logical relationship between a static magnetic field and one that occurs because an electrical field is moving?

[darkenlighten]

The simple, not too exciting answer is that a magnetic field is produced when you have a moving charge, aka a current. I'm not sure it can be explained any deeper that that, at least in simplicity.

Edited February 6, 2011 by darkenlighten

[davey2222]

I think there is this fundamental thing called the electric vector potential where the electric field can be derived from it in the presence of a charge. And if you view it from a moving reference frame then the electric field 'looks' like a magnetic field.

[davey2222]

I think there is this fundamental thing called the electric vector potential where the electric field can be derived from it in the presence of a charge. And if you view it from a moving reference frame then the electric field 'looks' like a magnetic field.

 

Sorry, I meant electrostatic scalar potential not vector potential.

[Sisyphus]

Is there any logical relationship between a static magnetic field and one that occurs because an electrical field is moving?

 

All magnetic fields are ones that occur because an electrical field is moving. If you're thinking of something like a bar magnet, then the motion is the spin of the electrons contained therein, all aligned in the same direction.

[lemur]

All magnetic fields are ones that occur because an electrical field is moving. If you're thinking of something like a bar magnet, then the motion is the spin of the electrons contained therein, all aligned in the same direction.

Ok, so "spin" refers to motion of the electron that causes an electric current, only one that doesn't move through a series of electrons/atoms? So when the spin of many electrons is aligned in a bar magnet, they are not moving current in the sense of linear current but rather many atomic-sized circuits? What causes this "current" to "flow" continuously around the nucleus? Momentum? Usually I think of a (DC) current as stopping once the positively charged pole is reached. Is the spinning electron like a microscopic AC current that keep oscillating due to its own momentum or something?

[Sisyphus]

It's not really like a circuit, and it's not atom sized. It's electron sized. It behaves just like a large charged body would if you were to rotate it. Spin is an intrinsic property of electrons. You can think of it as an irreducible quantum of angular momentum.

[alpha2cen]

It's not really like a circuit, and it's not atom sized. It's electron sized. It behaves just like a large charged body would if you were to rotate it. Spin is an intrinsic property of electrons. You can think of it as an irreducible quantum of angular momentum.

 

Is there no magnetic field near 0K?

[Oldman]

I agree with Swansont's answer.

Imagine you are moving with the charge; you won't detect magnetic field.

 

 

[evansste]

I have to agree most with @darkenlighten. Just as Newton's gravitational law describes the relationship between two massive objects and the force between them, Maxwell's equations explains the relationship between electricity, magnetism and light. It's a fundamentally observed phenomenon. To me, your question is like asking "why does matter have mass?" or "why does one plus one equal two?". Both have fundamental, yet simple answers. If I were to answer any of these questions, I'd simply say that it's because that's how God designed his universe, and mathematics is how we precisely describe such fundamental phenomenon. I recognize that it's not the answer that everyone would give, but it's the best one that I have. It's always possible that there's a more fundamental description behind current fundamentals. But at this time, I view all of these as fundamentals.

[altergnostic]

I like this kind of question, sometimes we forget what we don't know. We know that an electric current is made up of electrons - it is basically electron flow - but what makes up the magnetic field? And what the heck is charge? We know how a charged particle behaves and interacts with other particles, but what is + or - about it? Or rather, what motion/property/interaction/particle/state makes it negatively or positively charged?

And what gives mass to matter is also an amazing question. What is mass? What gives matter impermeability and solidity? What does mass do to generate gravity? How does it pull (newton) or deform spacetime (gr)? How is mass and inertia related? What is it about mass that makes it resist change? I think it was Maxwell that made a dimensional analysis on mass and found that it can be decomposed into M = L^3/T^2. This volume over time squared, basically - the eq. is m = 2(r^2)s/t^2). What accelerates about mass?

 

But back to magnetism, how does it create a pull? I would assume that both the electrical and magnetic fields are generated by the same (more) fundamental cause, which may be related to whatever it is that physically makes up the magnetic field - photons? Maybe a photon is not really a point particle (likely... a point should have no properties, since it is just a coordinate, a distance from an origin, a 0 by itself) and someday we'll find that it has mass and size and that it is the motions of these photons that cause the effects we see. And then we will ask what makes the photons move, why do they always move at c, yada.

[MigL]

A lot of very bright people are convinced that magnetic monopoles should exist, and are actively searching for them. They are predicted to be very massive and would only probably be found at the boundaries between different domains of the early universe where symmetry breaking occurred differently. I believe Alan Guth was working on the problem when he came up with inflation.

[derek w]

 

All magnetic fields are ones that occur because an electrical field is moving. If you're thinking of something like a bar magnet, then the motion is the spin of the electrons contained therein, all aligned in the same direction.

Does a moving electrical field also cause the spin of the electrons to align in the same direction?

[SomethingToPonder]

True, Proffesor feynman did a lot of work in this field and im currently reading his lectures, I was lucky enough to get lent the books from someone. It is very interesting.