# Magnetic dipole interaction

1. Feb 8, 2013

### darkdave

I am simulating protons and electrons in a simulator that runs 1 femto seconds per second up to 1 second per second. So it can accurately show the passage of charge particles through space with data being updated on their displacement, velocity and acceleration.

However I am now adding in rotational data. This means that I need to simulate angular momentum and torque.

How do I do this?

For the electron do I have to calculate the torque at the classical electron radius at each pole due to magnetic interaction with other charged particle poles?

2. Feb 8, 2013

### Staff: Mentor

In a classical simulation, particles cannot rotate. If you want "rotating" particles, you need quantum mechanics - and if spin is relevant, I would expect that everything else should use quantum mechanics as well.

3. Feb 8, 2013

### darkdave

I am aware of the quantum complication but at the same time i can still create a bhor model intepretation since i know the angular momentum of the particle and its mass and classical radius. I just need to know how to simulate the particles changing orientation due to torque caused by external magnetic fields. Wether i choose to show particles spinning or not is irrelevant to what im asking since all i should be concerned about is the angular momentum of the particle.

Last edited: Feb 9, 2013
4. Feb 9, 2013

### Staff: Mentor

The Bohr model works reasonably well for hydrogen-like atoms without spin, and nothing else, as far as I know.

For homogeneous fields, spin is irrelevant, and you just have the usual formula $F=q\vec{v}\times \vec{B}$.

5. Feb 9, 2013

### darkdave

What is the vector B representing in that formula?

6. Feb 9, 2013

### darkdave

ok i looked up that formula Force = charge velocity cross product magnetic field. The vector representing Magnetic field does it point to the center of the particle that acts like a magnet? For example is B pointing to the center of an electron if we are modeling 2 electrons that are interacting not just electrically but magnetically as well due to each of them having a magnetic field due to their intrinsic angular momentum

7. Feb 9, 2013

### darkdave

Also what if the velocity of the particle is ZERO? Isnt the current orientation more relevant here?

8. Feb 9, 2013

### darkdave

so think about it this way, we have 2 electrons each with a north and south magnetic pole and i want to simulate each electron turning its North Poles toward the other electron's South Pole. And each like poles repelling each other. So basicly i need to know torque.

9. Feb 9, 2013

### Staff: Mentor

No. A proper classical treatment would involve retarded potentials.
Don't forget the electric part, it will be retarded as well.
Then the force due to the magnetic field is zero.
Electric current implies a non-zero velocity, I don't understand the question.
Electrons do not have poles. And they cannot rotate in a classical way.

10. Feb 9, 2013

### darkdave

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

Also are you saying that an electron HAS NO ORIENTATION?

11. Feb 9, 2013

### Staff: Mentor

This is their spin, and it is not a classical property of the electron.
Not in the way that could always say "it points in this direction" in a meaningful way.
Electrons are point-like. What is the orientation of a point?

12. Feb 9, 2013

### darkdave

That link proves that Electrons have a MAGNETIC DIPOLE like MAGNETS. Meaning they have a NORTH AND SOUTH MAGNETIC POLE due to their "spin".

What I want to do is simulate electrons behaviour much like how real magnets behave when they are in close proximity. Their poles should point toward or away from other particle's dipoles.

13. Feb 9, 2013

### darkdave

Wiki says

The electron is a charged particle of charge (−e), where e is the elementary charge. Its angular momentum comes from two types of rotation: spin and orbital motion. From classical electrodynamics, a rotating electrically charged body creates a magnetic dipole with magnetic poles of equal magnitude but opposite polarity. This analogy holds as an electron indeed behaves like a tiny bar magnet. One consequence is that an external magnetic field exerts a torque on the electron magnetic moment depending on its orientation with respect to the field.

14. Feb 9, 2013

### Staff: Mentor

A magnetic dipole is not something with a north- and a south-pole. The dipole has an orientation, but that can be a superposition of multiple possible orientations, and the strength of the dipole, measured in an arbitrary direction, is always a fixed number (for electrons) and just the sign is variable. There is no way to model this classically.

I understand that you want to do that. But electrons do not behave like macroscopic magnets.

15. Feb 9, 2013

### darkdave

so what do you suggest is the best way to simulate electrons in as much classical way as possible?

I mean I know they dont have "spin": in the classic sense, but I can still make them spin based on known facts for example: the classical radius of the electron, the known mass and the known angular momentum. This way they behave in a way that is not true to reality but its still based on real data so intuitively it has some hidden truth.

What could I do for magnetic fields of the electron to do something similar to what i just proposed?

16. Feb 9, 2013

### Staff: Mentor

That depends on the setup you want to evaluate.

Well, you don't have the g-factor there, for example.

Depends on the setup.

17. Feb 9, 2013

### darkdave

can you propose a setup?

So far I know I want to show the electron spinning based on the available data of known intrinsic angular momentum, mass and classical electron radius. Can you use that as a setup? And fill in any blanks for me at your discretion.

I basicly want to show the particle changing orientation in real time in reaction to a neighboring particle's magnetic influence.

If it cannot be continuus then make compromises. I can make the particle perform discrete changes in orientation if need be. BUT I NEED A MODEL ANYKIND OF MODEL ASAP!! :)

18. Feb 9, 2013

### Staff: Mentor

I thought you want to calculate something. How can I guess what that is?

Are those particles slow (relative to the speed of light)? It might be possible to neglect any magnetic effects, as they have a relative influence of the order of v/c.

I doubt that the results will be good, but maybe you can add dipole-dipole interactions with the electron magnetic moment in a classical way. But if it does not influence anything, where is the point?

19. Feb 9, 2013

### darkdave

There may be thousands of particles in the simulation, each with a magnetic dipole. Inwhich case the effects i assume would be multiplied?

20. Feb 9, 2013

### Staff: Mentor

Or they could average out.

Again, it is impossible to be specific if you are so vague about the situation you want to simulate.