electric charge and magnetism

[gib65]

What's the difference between electric charge and magnetism?

[MrSandman]

I believe that electric charge has nothing to do with magnetism.

There is no electricity in magnets.

However, if your talking about the polarity both have it just in a diffent way. I had this in my freshmen year, so I don't remember much. Just thought I'd reply since no one else was.

[Mr Skeptic]

Magnetism is created by moving electrical charges. Electrical charges are monopoles, whereas magnets are always dipoles (they have a north and south but you cannot separate them). Electric field lines look like rays emanating from or ending at an electric charge; magnetic field lines look like closed loops.

[MrSandman]

Yeah, what he said. Magnets have to do with domains too. Mr Skeptic? Can you tell about domains? It has been too long.

[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.

[Mr Skeptic]

Yeah, what he said. Magnets have to do with domains too. Mr Skeptic? Can you tell about domains? It has been too long.

 

Certainly. Ferromagnetic materials have magnetized domains, which are like miniature crystals that are magnetic. The magnetism is due to the way electrons are arranged in the atom. In non-magnetized material, the domains are angled in all sorts of directions, and cancel each other out. You can draw this as little arrows in all sorts of directions. In magnetized materials, the domains are aligned in (more or less) the same direction. You can draw this as several arrows all in the same direction.

 

You can temporarily magnetize something ferromagnetic by doing the following:

place it in a magnetic field (temporary)

leave it in a magnetic field for a while (stronger magnetic field for shorter times)

heat it and let it cool in a magnetic field.

rub a magnet across it in the same direction (or opposite direction with the other pole)

[Klaynos]

Your getting into opinions not fact Severian.

 

I seriousely suggest you reconsider that, the maxwell equations when applied to magnetodynamics clearlly show that what Severian said is infact true...

[Mr Skeptic]

I don't think that you can eliminate all magnetic fields by simply changing your frame of reference. What about an electron's magnetic dipole moment? That's due to angular momentum.

[Klaynos]

Is the dipole an external magnetic field? If so from memory a reference frame change can transform it into an electric field.

[ydoaPs]

I seriousely suggest you reconsider that, the maxwell equations when applied to magnetodynamics clearlly show that what Severian said is infact true...

 

[math]{\nabla}{\cdot}{E}=\frac{\rho}{\epsilon_0}[/math]

 

[math]{\nabla}{\cdot}{B}=0[/math]

 

[math]{\nabla}{\times}{E}=-\frac{\partial{B}}{\partial{t}}[/math]

 

[math]{\nabla}{\times}{B}={\mu_0}{J}+{\mu_0}{\epsilon_0}{\frac{\partial{E}}{\partial{t}}}[/math]

 

Where [math]\rho[/math] is electric charge density, B is magnetic field, E is electric field, [math]\epsilon_0[/math] is permittivity of free space, [math]\mu_0[/math] is magnetic permeability of free space, J is current density, and t is time.

[MrSandman]

One thing you have to consider is that electrical currents aren't always magnetic currents. But maybe maybe the opposite is true. When electrons flow through a metal I call that electrical current not magnetic. There is a defining point and it isn't just a perspective. Will other magnetic material be attracted to the electrical current going through the wire? No. That is why you got the two different names. Then there is the combination of the two electromagnets.

 

yourdadonapogos, please tell me what you are trying to prove by the formula. Like stating what the formula is for.

I see that your a scientist, but I think I have a point. Mr Skeptic could probably explain better.

 

Thanks for the refresher course on magnets. It was what I remembered, but I wasn't sure.

[ydoaPs]

One thing you have to consider is that electrical currents aren't always magnetic currents.

No? Could you do two things for me? The first is show, using the equations I provided above, how that is possible. The second is provide an example.

 

There is a defining point and it isn't just a perspective.

What is this defining point?

 

Will other magnetic material be attracted to the electrical current going through the wire?

Yes. How do you think electromagnets work?

 

yourdadonapogos, please tell me what you are trying to prove by the formula. Like stating what the formula is for.

Those four formulas are the Maxwell equations spoken of earlier in the thread. That is why I used the quote I did. I'll explain what they mean, but it would be easier for both of us if you would first tell me your level of maths.

 

 

http://en.wikipedia.org/wiki/Maxwell_equations

[MrSandman]

What is the defining point?

 

The defining point is that one is magnetic and the other is electrical.

 

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.

 

I'm sorry about asking about the formula. I sorry you took it as an attack. I didn't relize what it was. Thanx for the link. I'm only a college algebra student. If there are the same thing then tell me why they aren't the same name. I like to be corrected that is what my professor like about me. However, they like how I don't settle for a "This is how it is." response. Please, explain. I came to this forum to learn, not just to say, "Your wrong".

 

Is the dipole an external magnetic field? If so from memory a reference frame change can transform it into an electric field.

 

You use the word transform. That means they're are different right?

[iNow]

Please, explain. I came to this forum to learn, not just to say, "Your wrong".

It's useful if you soften your tone, and don't present everything like you know it already. You basically pissed on the equations presented, and didn't realize they were the work of JC Maxwell which have stood the test of time and really are considered amazing. Remain open to the fact that you might be wrong, and often are. Also, it's not "your wrong," it's "you're wrong," as in "you are wrong."

[Mr Skeptic]

OK, say you have 3 electrons moving along the x axis at .1c, .2c, and .3c. From what perspective can you look at this and say there is no magnetic field?

[MrSandman]

Ha, thanx, I always make stupid mistakes when posting. Tone is important, I'll remember that kind sir.

 

I didn't mean to come across that way. Maybe I should change my signature to.

 

I'm never mad at you, I'm just not good with tone when posting. I love science and want to know more.

 

OK, say you have 3 electrons moving along the x axis at .1c, .2c, and .3c. From what perspective can you look at this and say there is no magnetic field?

 

You talking to me?

[gib65]

Magnetism is created by moving electrical charges.

 

So does that mean that the magnets on my refridgerator have electrons moving about inside (or something else eminating electric charge)?

[MrSandman]

Good question. Anyone have an answer???

[Mr Skeptic]

So does that mean that the magnets on my refridgerator have electrons moving about inside (or something else eminating electric charge)?

 

Yes. Normally the effects cancel out, but not in a magnet.

[MrSandman]

Does this have to do with Ionic bonds?

[Cap'n Refsmmat]

Ionic bonds have an electrostatic attraction between atoms (meaning one has a positive charge, one has a negative charge). This is similar to, but not the same as, magnetism.

[MrSandman]

Oh, so how does magnetism work differently. Please, wise one, I live to absorb your knowledge for my own.

 

No sarcasm intended.

[gib65]

Yes. Normally the effects cancel out, but not in a magnet.

 

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)?

[Severian]

To clarify my earlier statement, one can write Maxwell's equations in a covarient form as [math]\partial_\mu F^{\mu \nu} = j^{\nu}[/math] where [math]j^{\nu}[/math] is the 4-current (i.e. charge density in the time component and three-dimensional charge current in the space componenets), and [math]F^{\mu \nu}[/math] is the field strenght tensor.

 

[math]F^{\mu \nu}[/math] can be written in terms of the Electric and Magnetic fields, according to:

 

[math]F^{\mu \nu} \equiv \left( \begin{array}{cccc}

0 & -E_1 & -E_2 & -E_3 \\

E_1 & 0 & -B_3 & B_2 \\

E_2 & B_3 & 0 & -B_1 \\

E_3 & -B_2 & B_1 & 0

\end{array} \right)[/math]

 

[math]F^{\mu \nu}[/math] is a second rank tensor under the Lorentz group, so if you perform a Lorentz transformation [math]\Lambda[/math] then [math]F^{\mu \nu} \to \Lambda^{\mu}_{\:\:\alpha} \Lambda^{\nu}_{\:\:\beta} F^{\alpha \beta}[/math].

 

Thinking in terms of matrices, this mixes the time-like and space-like parts of the matrix up (similarly to how a rotation mixes the rows and columns up) and therefore a pure electric field in one frame can look like a magnetic field in another.

 

Notice that I never said that you could find a frame where all electric look magnetic. The point here is that magnetic fields are the relativistic completion of electric fields.