# Why does a magnetic field repel moving charges?

1. Jan 31, 2013

### quantumfoam

Why does a magnetic field produce a force on a moving charge? I would love if someone answered why and not how.

2. Jan 31, 2013

### Staff: Mentor

Are you familiar with the equation for the Lorentz force?

3. Jan 31, 2013

### quantumfoam

Yes I am.

4. Jan 31, 2013

### ModusPwnd

Surely that is not an explanation of "why", but rather an explanation of "what" or maybe "how".

Asking "why" is not always useful in science, particularly not for the fundamental phenomenon which physics specializes in. When you ask why what you normally get is an explanation of the phenomenon "one level" deeper. This fails where you are at the bottom level. Ask why the sun rises and sets, get a slightly deeper explanation involving the orbit of the earth. Ask why the orbit of the earth, get a deeper explanation of mass and gravity. Ask why does mass get attracted by gravity, there is no answer. And of course there can be no answer, it is a "fundamental" phenomenon.

The lorentz force is the same way, its a fundamental phenomenon. There is no lower level science to appeal to for an explanation of why. We observe the interactions and describe/predict them with our theory. What other possible thing could be done? Nothing.

Now if there ever comes a time when we do have an answer for "why the lorentz force" or "why the gravitational force" then these cease to be fundamental low level phenomenon. There would then be a new more fundamental set of behaviors that would be completely resistant to any question of "why".

5. Jan 31, 2013

### quantumfoam

Thank you so much! You can make good explanations(: So as far as we know, know one knows why a moving charge is repelled by a magnetic field?

6. Jan 31, 2013

### 256bits

"... why a moving charge is repelled by a magnetic field?"
Repelled is not a very good word to use.
Repel means to resist, to ward off, to thrust backwards.

If the charge is travelling parallel to the magnetic lines of force there is no effect upon the velocity of the charge. If the charge is travelling perpendicular to the magnetic field then the charge will have a maximum change in velocity of direction but not magnitude.

Are you familiar with the Lorenz force?
http://en.wikipedia.org/wiki/Lorentz_force

7. Jan 31, 2013

### Staff: Mentor

8. Jan 31, 2013

### quantumfoam

Yes.

9. Jan 31, 2013

### quantumfoam

Lol I understand the Lorentz force. I just want to know if in the world of physics, is there a reason why a moving charge interacts with a magnetic field the way it does.(:

10. Jan 31, 2013

### FeynmanIsCool

Physics doesn't really answer "why" questions. Physics does not say why electric and magnetic fields interact, but rather how they interact.

11. Jan 31, 2013

### quantumfoam

I know but I was wondering if there was any deep explanation for why it happens. But the answers I have obtained here are more than I wanted(: Thank you guys!

12. Feb 2, 2013

### 256bits

Resonant theory in action on PF.

13. Feb 3, 2013

### sophiecentaur

Watch what Mr Grumpy himself had to say about all this. (No, I love him, really!)

14. Feb 3, 2013

### quantumfoam

He is awesome! Thank you sophiecentaur!

15. Feb 3, 2013

### FeynmanIsCool

I almost posted this! haha

16. Feb 3, 2013

### quantumfoam

He is pretty awesome!(:

17. Feb 3, 2013

### sophiecentaur

He had a colourful life, too. Not just Physics, you know.

18. Feb 3, 2013

### quantumfoam

I heard he was a great artist. I wish I could have seen some of it. I would imagine his artistic work to be as great as his radical ideas and his amazing ability to provide insight to our world over problems.

19. Feb 14, 2013

### quantumfoam

I recently stumbled into a Youtube video of a man explaining why a magnetic force on a moving charge appears. He said it was due to the interactions between the charges magnetic field and the external magnetic field. Is this true? I am not sure because he has posted a bunch of very helpful videos on electromagnetism. I don't expect him to be some sort of crackpot theorist.

20. Feb 15, 2013

### sophiecentaur

That's one way of looking at it. The other way is to consider the relativistic effect on the charges that are moving to set up the magnetic field (e.g. electrons moving in the wires of an electromagnet.). That way, it can all be explained in terms of electric forces. The alternatives are all valid, apparently.