electric charge and magnetism

[swansont]

Metal won't be attracted to electrical current. Unless you have the combination that is how it works. Run a open electrical current and try to have a paper clip stick to it. It doesn't work. That's why there is a combination called a electromagnet. I see that they are very similiar, but not exactly the same, or there wouldn't be a difference in names probably, even if the react in the same ways. When you look at a magnet you don't call the field an electric field you call it a magnetic. The are however very symmetrical.

 

An electromagnet is just electric current. There may be an iron core to concentrate the flux lines, but that is not typically a source of magnetic field. The difference is in how much field you can get by having multiple turns of wire vs a single pass.

 

Oh, of course, the electrons orbit their nuclei; I never thought of this until you put it the way you did. So what's unique about the motion of electrons in a magnet? Do they have more of a uniform pattern of motion (like most in the same direction)?

 

A valence electron is going to have a magnetic moment from the spin and orbital angular momentum. If that's unpaired, you get a net field from the atom. If the physical structure of the material is such that a lot of the atoms can align so that the fields add you get a magnet, otherwise they will cancel out. In some materials the atoms can align in the presence of an external field, and either aligning or anti-aligning with it. In ferromagnetic materials, you can freeze those atoms in place to give you a magnet; there is some physical difference between thos orientations so the material expands/contracts in different directions as you do this (magnetostriction) which gives rise to the humming sound you can hear from transformers.

[Farsight]

Time to dredge up one of my essays, chaps.

[gib65]

A valence electron is going to have a magnetic moment from the spin and orbital angular momentum.

 

So then what determines the polarity of the magnet? Is it the direction of spin or angular momentum?

[Klaynos]

SO I think Severian and Swansont cleared up the points I originally wrote to go in this post... lol

 

So then what determines the polarity of the magnet? Is it the direction of spin or angular momentum?

 

Yes, the it depends on the direction of the dipole moment of the atoms in the material.

 

When you magnetis a lump of say iron, you force all the dipole moments to align a certain way. It then takes energy for these to disalign with each other, so with no outside influences the lump (yes lump is a technical term) remains magnetised.

[gib65]

Very interesting.

 

Now I've heard that the relation between electric charge and magnetism goes both ways - that is, that a moving electric charge creates a magnetic field, and a moving magnetic field creates an electric charge. I also heard that Maxwell proposed that this is what accounts for the propagation of electromagnetic waves through space - that is, a moving electric charge creates a magnetic field surrounding it, and since this field would have to be moving with the electric charge, it in turn creates more electric charge surrounding it, which in turn is also moving and therefore creates another magnetic field surrounding it, and that in turn creates an electric charge, and so on.

 

Is this how it works?

[MrSandman]

You said that it has to have an Iron core, so your still just saying they are related through a transitive property. Aluminum, is a metal that can have current, but isn't magnetic. Why is that? Severian, I didn't realize your exprience. Sorry, about the comment. I guess MrSandman inserted his foot into his mouth.

[insane_alien]

if you run a current through aluminium you will get a magnetic field. it cannot be naturally ferromagnetic(like iron) because of it's orbital structure, it does exhibit diamagnetism like all elements though.

 

just because an electromagnet has a ferromagnetic core does not mean that the core is required for it's function. ferromagnetic materials(not always iron, there are others) can intensify the field. kind of like a magnetic magnifying glass.

[Klaynos]

Very interesting.

 

Now I've heard that the relation between electric charge and magnetism goes both ways - that is, that a moving electric charge creates a magnetic field, and a moving magnetic field creates an electric charge. I also heard that Maxwell proposed that this is what accounts for the propagation of electromagnetic waves through space - that is, a moving electric charge creates a magnetic field surrounding it, and since this field would have to be moving with the electric charge, it in turn creates more electric charge surrounding it, which in turn is also moving and therefore creates another magnetic field surrounding it, and that in turn creates an electric charge, and so on.

 

Is this how it works?

 

Pretty much, it's described as boot strapping.

 

if you run a current through aluminium you will get a magnetic field. it cannot be naturally ferromagnetic(like iron) because of it's orbital structure, it does exhibit diamagnetism like all elements though.

 

just because an electromagnet has a ferromagnetic core does not mean that the core is required for it's function. ferromagnetic materials(not always iron, there are others) can intensify the field. kind of like a magnetic magnifying glass.

 

At room temperature.

 

It's to do with the energy levels of the atoms. You can get more spin up than spin down electrons... The curie temperature of most materials is such that at room temperature they are not magnetic.

[MrSandman]

Ok, however what is the difference with something that is naturally ferromagnetic and Metals that can become magnetic. Is it just that all the domains are natural aligned in ferromagnets to make them polar.

[swansont]

Very interesting.

 

Now I've heard that the relation between electric charge and magnetism goes both ways - that is, that a moving electric charge creates a magnetic field, and a moving magnetic field creates an electric charge. I also heard that Maxwell proposed that this is what accounts for the propagation of electromagnetic waves through space - that is, a moving electric charge creates a magnetic field surrounding it, and since this field would have to be moving with the electric charge, it in turn creates more electric charge surrounding it, which in turn is also moving and therefore creates another magnetic field surrounding it, and that in turn creates an electric charge, and so on.

 

Is this how it works?

 

A moving/changing magnetic field creates an electric field, not a charge. And yes, you can get a wave solution from Maxwell's equations, and it was eventually realized that light was an electromagnetic wave.

[MrSandman]

What about my question?

[Klaynos]

Ferromagnetic materials are things which can remain magnetic (normally at room temperature) when an external field is turned off.

 

Other materials have no magnetic effect (unless a current is being past through them) without an external field being applied.

[MrSandman]

Okay, that makes sense. They could become unmagnetized through physical shock, and by the change of temperature?

[Klaynos]

Okay, that makes sense. They could become unmagnetized through physical shock, and by the change of temperature?

 

Physical shock could do it. But they are in a low energy state when they are aligned, to unalign them the best way is to apply very large magnetic fields that oppose the static field of the material. Of course doing that you risk magnetising the material inline with the applied field.

 

Basically every time you extract some energy from the magnet (say by lifting a metal bar with it) you have to get that energy from somewhere and that is from the dipole moments.

[swansont]

Physical shock could do it. But they are in a low energy state when they are aligned, to unalign them the best way is to apply very large magnetic fields that oppose the static field of the material. Of course doing that you risk magnetising the material inline with the applied field.

 

 

What you typically do is use an oscillating field. Either really fast, so not all the domains have time to react, and you randomize the domains so that they cancel, or with a slower field (we just use 60Hz in the lab with our degauss-o-tron) that you reduce in strength slowly. Basically you'll freeze in the earth's field (or any other residual field present) if you do it in an unshielded area.

[gib65]

Pretty much, it's described as boot strapping.

 

Okay, so let's take this image as an example:

 

 

We see that the iron filings have alinged themselves along those archs which I'm assuming are the magnetic fields. Would the electric fields be the areas in between (i.e. the white archs where no iron filings seem to exist)? If I took a bucket full of protons () and dumped them onto this magnetic bar, would they settle along the white archs between the iron filings?

[insane_alien]

no, the filings group into lines because they themselves become magnetised. there is still a magnetic field within the gaps.

 

to have an electric field you would need to apply a charge to the magnet.

[Farsight]

LOL, this thread! I'm still laughing at:

 

Severian: Electric fields and magnetic fields are actually the same thing - the difference is only a point of perspective. A pure electric field to one observer may be a magnetic field to a different observer.

 

MrSandman: Your getting into opinions not fact Severian.

 

gib65: listen up. An electric field is the same thing as a magnetic field. That's why we call it an electromagnetic field. A magnetic field is how you see an electric field if you're moving through it. Or if it's moving through you. An electric field is a "twist field". It's twisted space. A magnetic field is a "turn field".

 

Imagine that you’re flying through space like an aeroplane with your arms outstretched, but the space ahead of you is twisted like a catherine wheel because an electric field is present. When you encounter the twisted space, your wings will tilt. The twisted space will make you rotate. In other words it will cause you to turn. Now use Relativity to work out that if you aren’t travelling through space but you find yourself turning, then the twist must be travelling through you. That's all it is. It's as simple as that. Inside that magnet there are electrons travelling around in little weeny circles, all going the same way, and they're like the earth going round the sun. A day lasts 23 hours 56 minutes not 24 hours. There's a little bit of "turn" left over. So you get some of it spilling out, and voila you've got a magnetic field.

 

You can think of a battery to a clockwork spring, but where the twist is in space rather than in steel. The electric twist extends forward with a flowing current, and causes a turning motion akin to a pump-action screwdriver, so demonstrating the principle of the electric motor. But we can equally turn a screw with a manual screwdriver, extending the twist forward, so demonstrating the principle of the dynamo. Applying a forward motion to the twist achieves a turning motion, and vice versa.

 

Cross my heart and hope to die, that's how it is.

[gib65]

no, the filings group into lines because they themselves become magnetised. there is still a magnetic field within the gaps.

 

to have an electric field you would need to apply a charge to the magnet.

 

Hhm... I'm trying to find the right kind of visualization of this phenomenon. I'm taking the "leap-frog" image of magnetic waves creating electric waves creating magnetic waves... and there you have the propagation of electromagnetic waves through space. Do the magnetic and electric fields correspond to the crests and troughs of the waves? I thought the example of the iron bar might suggest they exist as a standing wave, but I guess not. Light moves, obviously, so the crests and troughs must also move through space, right?

[Mr Skeptic]

Magnetic field lines "flow" through some materials, like iron, better than they do through air. Also, when in a magnetic field, the iron becomes magnetized. The direction of the magnetism is that of the magnetic field, resulting in attraction. That is why iron is attracted to a magnet, and also why you can build chains of paper clips longer than what the magnet alone could lift a paper clip. Anyhow, you can think of the filings as a bunch of tiny magnets which point along the magnetic field lines.

 

Electric charge plays no part in all this except as stated previously, in that it is responsible for the magnetism in the first place.

[insane_alien]

okay, gib.

 

static magnetic fields do not create electric fields(and vice versa) but a changing magnetic field will create an electric field(and vice versa).

 

the case of the prmenent magnet is of a static field.

[losfomot]

Like AI just said... a magnet sitting still on the table in front of you does not create an electric field because it is not moving relative to you. Take a magnet and an electrical wire. place them beside each other on the table and there is no electric current flowing through the wire... but if you pick the wire up and sweep it past the magnet lengthwise, a current will run through the wire. This is what is meant by 'frame dependent'... The magnet has a magnetic field in one frame and an electric field in another frame (the frame that is moving relative to the magnet)

 

(I hope this is correct, I'm no expert I'm just trying to help convey the idea in an understandable way)