# Magnetic field direction

1. Oct 28, 2008

### nemesiswes

why do magnetic fields always go from south to north or whichever it was. i heard that in quantum mchanics, electric and magnetic fields use photons as there force carrieres and i was wondering if thats true then why does a magnetic field always have to have both???

if anyone knows of a really good site that goes indepth on how that stuff works then that would help, i already tryed wikipedia and some others but not enough info

2. Nov 2, 2008

### pallidin

I don't think magnetic fields use photons as their force carrier. Maybe virtual photons, but my understanding is that its still a mystery.

With respect to N-vs-S, I don't know. I think its just a convention that came about from navigation.

3. Nov 2, 2008

### mym786

The resson behind any type of forces is exchange particles. Exchange particles are particles when they are exchanged, they give attraction or repulsion.Moreover, there are four fundamental forces in nature. They are Strong nuclear forces , Electrmoagnetic forces , weak nuclear forces and gravity forces.

Electromagnetic force use photons as there exchange particles. Now how does an exchange particle work.
Imagine you and you friend are standing facing each other on a frictionless surface and you throw a ball. The ball will give you a backward push, also your friend will move backward when he catches the ball.
Now Imagine both of you standing facing oposite to each other, and you throw the ball. In this case you will be pushed backwards(in the direction of your friend) and also your friend when he recieves the ball will be pushed backwards when he recieves the ball.

In case 1 you result a repulsive force and in case 2 you get an attraction force.

4. Nov 4, 2008

### john 8

How would your friend catch the ball if you are not throwing the ball in his direction?

5. Nov 4, 2008

### john 8

Particles of what? Are you suggesting a magnet is giving off particles?

My question in regards to this whole electromagnetic field theory is the idea of frequency.

Light for example is an electromagnetic wave of different frequencies, what exactly is doing this traveling of the up and down motion?

We know that an object in motion will travel in a straight line until acted upon by an outside influence. So what is causing this constant change of direction of this energy? What keeps this frequency stable and precise, no decay over time and distance.

6. Nov 4, 2008

### Phrak

Magnetic fields are not something like a fluid that is exuded from one pole and absorbed in another. If you were to define the directioin of the magnetic field for the first time, you could just as well have defined the field as pointing in the other way and all your equations about magnetism would still work. There would just be a negative sign in a few places that differed.

7. Nov 5, 2008

### wysard

Mym768, I'm confused. If you used real photons for energy exchange (as opposed to virtual ones) then if you put two rare earth magnets close to each other with a strain gauge attached to each on you could measure the strength of thier attraction. Then place a large area piece of bristol board between them you could watch the strain guage fall to virtually zero. Since this clearly doesn't happen is there another explanation, or am I not following a critical piece of your logic?