# What make the magnet to be magnet with magnetic field?

1. May 14, 2007

### scientist91

Last edited: May 14, 2007
2. May 14, 2007

### Hootenanny

Staff Emeritus
Scientist, I again reiterate what I said in your previous thread; forums are not an ideal medium from which to learn basic physical principles, you would be much better served with an elementary undergraduate physics book. That said I offer a brief summary of magnetism.

Magnetism is a direct affect of atomic magnetic dipoles, which itself results from two quantum mechanical properties of atomic electrons. Firstly, the electron has an orbital angular momentum which is determined by orbital angular momentum quantum number which falls out of the Schrödinger Equation. This "orbital angular momentum" should not be confused with classical angular momentum in so much as electrons in an atom do not obey classical orbits. This orbital angular momentum results in an orbital magnetic dipole moment which behaves as a classical magnetic dipole moment (think tiny bar magnet).

The second, more dominant factor, is the electron "spin". Again, this spin should not be confused with classical spin (the electrons in an atom don't actually spin on their axis), it is merely a quantum mechanical description of the electron state. Again, this spin quantum number results in a spin magnetic dipole moment.

Now, to occupy the lowest energy states (magnetic dipole moments have an associated potential energy in the presence of a magnetic field) the electrons tend to 'pair up' with other electrons so that their magnetic moments cancel each other out in a full shell/sub shell, it is the partially filled shells/sub shells which result in a net magnetic dipole moment. The atomic dipole moment is simply the sum of all the individual orbital and spin magnetic dipole moments. Therefore, elements / substances with certain configurations / partially filled shells will be magnetic.

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magmom.html" [Broken] (better than wiki)
http://en.wikipedia.org/wiki/Magnetic_moment" [Broken]

Last edited by a moderator: May 2, 2017
3. May 15, 2007

### scientist91

Ok, man thank you. I know the basics of the physics, but it is hard for me to understand on the English language because it is not my first language. I am from Macedonia so it is hard for me to translate and understand what you're saying, and also I don't know the conceptions on English language. And do u have any picture of that orbital angular momentum? Where do the electrons are moving, different orbital or something? Why some magnetised materials lose their magnetic field? What make the electrons to have that orbital angular momentum?

Last edited by a moderator: May 2, 2017
4. May 15, 2007

### ZapperZ

Staff Emeritus
If you have a problem in trying to ask a question, and you also have a problem in understanding the answers you were given, don't you think this whole exercise is becoming rather futile?

Here's what I strongly suggest that you do:

1. Read the references given, especially at Hyperphysics.

2. Now, using THOSE references, try to understand the relevant sections that could answer your questions.

3. After you have made an effort to understand those, and if you still could not figure those out, ONLY THEN should you ask here. But don't ask some basic, generic question that requires a whole lesson in physics to understand. That is impossible to do on a forum like this. Ask the specific item that you read that you did not understand. Give the exact reference and the exact location what and where you did not understand.

If not, I don't think anyone has the patience to want to teach you whole textbooks worth of physics. I certainly don't.

Zz.

5. May 15, 2007

### scientist91

I can't understand so help me.

6. May 15, 2007

### Hootenanny

Staff Emeritus
To reiterate what Zz is saying and what I have said previously; Forums are not suitable mediums for learning new concepts or material, they are very good if you have specific questions regarding specific parts of physics. You have my sympathy, but this is compounded by the language barrier between a predominantly English speaking forum and your own native language.

What you are essentially asking me/us to do is present virtually whole lectures on parts of physics where you have little or no grounding, this is a virtually impossible task on a forum and even if it were, I am not willing to invest the and effort that it would take. Now, I don't mind offering help to those who have fairly specific questions, and I don't mind writing extended posts, I usually have PF open while I'm working and just check for new posts every now and again; but what your asking is for us to basically write a physics textbook for you. I'll repeat again, you would be best served purchasing an elementary physics textbook or at least reading the references I gave you because from your questions it doesn't seem to me that you have read the links.

Again, I sympathise with your language barrier but you would be best served with a textbook (or at least reading the references).

7. May 17, 2007

### scientist91

and is the magnetic field energy?

8. May 17, 2007

### Hootenanny

Staff Emeritus
The magnetic field is not actually energy itself; the magnetic field is a pseudo-vector field, that is, it is just a way of associating a vector with a given point in space. However, magnetic [and electric] fields can store energy such as in an inductor[or capacitor in the case of an electric field]. The energy density (U/V) in a magnetic field (B) can be calculated thus;

$$\frac{U}{V} = \frac{B^2}{2\mu}$$

You should realise that the magnetic field is simply a relativistic consequence of the electric field.

P.S. There's no need to tack your question onto the bottom of another [unrelated] thread; you should post new questions as new topics. Thanks

Last edited: May 17, 2007
9. May 17, 2007

### scientist91

Ok, but I don't want to post every topic for every question, so I am searching for similar topics. So how it stores energy?

10. May 17, 2007

### Hootenanny

Staff Emeritus
Last edited by a moderator: Apr 22, 2017
11. May 17, 2007

### scientist91

Why the magnet attract iron and why the magnet is not attracting wood?

12. May 17, 2007

### Hootenanny

Staff Emeritus
Why do you think that a magnet attracts iron but not wood?

13. May 17, 2007

### scientist91

try you will see. btw-when the magnetic field is making the electrons obey their upper orbital and make energy circle and then when they release their energy, go down.

14. May 17, 2007

### Hootenanny

Staff Emeritus
No, you try and see. I expect you to show a little effort to understanding the material. :grumpy:

15. May 18, 2007

### scientist91

And then which orbitals they obey?

And then on which axis they spin?

16. May 18, 2007

### jackiefrost

Hootenanny - could you explain a little more about why you used the term "pseudo-vector field" to describe the magnetic field? Because of its relativistic nature? Thanks.

17. May 18, 2007

### Hootenanny

Staff Emeritus
I was simply trying to say that the electrons do not 'orbit' around the nucleus as you would probably imagine. Rather there is some non-zero probability that they exist at some distance from the nucleus; the most probable position [for a given energy level] corresponds to a circular ring around the nucleus somewhat like a classical orbit. However, for any given energy level (n) [and low orbital quantum number (l)], there is some non-zero probability that the electron can be found very close to the nucleus. Therefore, it is best not to say that electrons orbit around the nucleus, rather there is some probability to find an electron somewhere in the electron 'cloud' around the nucleus. I'm afraid that this is elementary QM and will probably seem very 'weird' and counterintuitive if you are encountering it for the first time.
They don't spin at all.

18. May 18, 2007

### scientist91

Look man, when there is magnetising the electrons from the lower orbitals gain energy and go into the upper orbitals, so they are spining around the nuclei (circular spinning), and when they release their energy, then they make circle of energy, that is the magnetic field, and then (after they released their energy) go into the lower energy level so the magnetic field is around the electrons

19. May 18, 2007

### Hootenanny

Staff Emeritus
A pseudo-vector is different to a true or "proper" vector in that when we invert the coordinate axes a true vector is transformed into its negative, whereas a pseudo-vector remains unchanged; the cross product of two vectors is a pseudo-vector where as the triple cross product is a true vector. Originally, the Maxwell equation were written in vector form using dot and cross products. The vector form of Maxwell's equations are invariant under rotations, but not under [Lorentz] boosts. Using the vector form of Maxwell's equations we can describe the magnetic field as a pseudo-vector. However, in the modern formulation of Maxwell's laws, using Clifford Algebra, we can combine all Maxwell's equations into a single form;
$$\nabla F = \frac{J}{c\epsilon_0}$$
This form has the advantage of both being easier to remember, and being Lorentz invariant. In this form we represent the magnetic field as a bi-vector, which is if you like the 2D analogue to a 1D vector, imagine a plane[bi-vector] vs. a line [vector]. Technically, a bi-vector is a 2nd rank tensor in 3D space; tensors are just generalisations of vectors which can be written in concise notation.

I hope that was somewhat helpful

http://www.av8n.com/physics/maxwell-ga.htm" [Broken]
http://mathworld.wolfram.com/Pseudovector.html" [Broken]
http://mathworld.wolfram.com/Tensor.html" [Broken]

What you have [loosely] describe there is the Bohr model, which is a very crude approximation of what actually happens at the atomic level. If you like I could give you some more links to website that offer some basic description of quantum mechanics (hyperphysics is quite good); but as I said before, you really need a textbook.

Last edited by a moderator: May 2, 2017
20. May 18, 2007

### scientist91

But do you actually agree with me, is that true what am I saying?

21. May 18, 2007

### Hootenanny

Staff Emeritus
Re-read the above post. You have described the Bohr model, which is a somewhat crude approximation to what actually happens at the atomic level. The Bohr model is a good place to start with the view of learning quantum mechanics; however, it is not a true description of what happens at the atomic level. For a better description you need quantum mechanics.

22. May 18, 2007

### Hootenanny

Staff Emeritus
I think thats a little unfair, I agree with Zz that it is impractical to present an entire introduction to physics on a forum, which is what this is turning into.

23. May 18, 2007

### jackiefrost

Wow! This sounds interesting. Thanks for putting me on to it. I'm in the midst of studying Maxwell's equations (via Feynman Lectures vol 2, Griffith, and the two volume Dover set of Maxwell's original presentation). I'm grateful for some new avenues to explore, though I'm only a newbie with tensors. Thanks for the links.

BTW - Is their such a thing as tensor fields (analogous to vector fields)? Also, is their any gravitational analogue to magnetism? That is, does a changing gravitational field or maybe the relative motion of mass (analogous to charge current) "produce" any additional component(s) to the gravitational field analogous to the role of magnetism in electrical phenomena?

jf

24. May 19, 2007

### mcstar

hi!

jackiefrost:
yes, there are tensor fields, the aforementioned F is itself a tensor field,
that is a physical quantity which can be described with its components,
with two indices, and is invariant under special transformations, and can
vary from point to point in space and time.

there are other examples, eg. the stress tensor:
Ci,j,k,l, and σi,j=Ci,j,k,lεk,l,
so C is a fourth-rank tensor.