Why does a magnetic field repel moving charges?

In summary, the question of why a magnetic field produces a force on a moving charge is a fundamental one in physics and does not have a definitive answer. The Lorentz force equation and the concept of electric and magnetic fields can be used to describe and predict the phenomenon, but the underlying reason for this interaction is still unknown. Some explanations point to the interactions between the charge's magnetic field and the external magnetic field, while others consider the relativistic effects on the moving charges. Ultimately, it remains a fundamental phenomenon in physics that may not have a deeper explanation.
  • #1
quantumfoam
133
4
Why does a magnetic field produce a force on a moving charge? I would love if someone answered why and not how.
 
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  • #2
quantumfoam said:
Why does a magnetic field produce a force on a moving charge? I would love if someone answered why and not how.

Are you familiar with the equation for the Lorentz force?
 
  • #3
Yes I am.
 
  • #4
berkeman said:
Are you familiar with the equation for the Lorentz force?

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
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
"... 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 traveling parallel to the magnetic lines of force there is no effect upon the velocity of the charge. If the charge is traveling 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
 
  • #8
Yes.
 
  • #9
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
quantumfoam said:
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.(:

Physics doesn't really answer "why" questions. Physics does not say why electric and magnetic fields interact, but rather how they interact.
 
  • #11
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
berkeman said:
There's an echo in here... :smile:

Resonant theory in action on PF.:redface:
 
  • #13
quantumfoam said:
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!
Watch what Mr Grumpy himself had to say about all this. (No, I love him, really!)
 
  • #14
He is awesome! Thank you sophiecentaur!
 
  • #15
sophiecentaur said:
Watch what Mr Grumpy himself had to say about all this. (No, I love him, really!)

I almost posted this! haha
 
  • #16
He is pretty awesome!(:
 
  • #17
He had a colourful life, too. Not just Physics, you know.
 
  • #18
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
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
quantumfoam said:
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.
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.
 

1. Why does a magnetic field repel moving charges?

The phenomenon of a magnetic field repelling moving charges is explained by the principle of electromagnetic induction, which states that a changing magnetic field induces an electric field. This electric field then exerts a force on the moving charges, causing them to be repelled from the magnetic field.

2. How does the strength of the magnetic field affect the repelling force on moving charges?

The strength of the magnetic field has a direct effect on the repelling force exerted on moving charges. The stronger the magnetic field, the greater the force exerted on the charges. This is because a stronger magnetic field will induce a stronger electric field, resulting in a greater repelling force.

3. Can a magnetic field repel both positive and negative charges?

Yes, a magnetic field can repel both positive and negative charges. This is because both positive and negative charges have a property called spin, which is a type of angular momentum. When these charges are in motion, they create a magnetic dipole, which interacts with the external magnetic field, resulting in a repelling force.

4. How does the direction of motion of the charges affect the repelling force?

The direction of motion of the charges is crucial in determining the direction of the repelling force. The repelling force is always perpendicular to both the direction of the magnetic field and the direction of motion of the charges. This means that if the charges are moving parallel to the magnetic field, there will be no repelling force.

5. Is there a limit to the speed at which moving charges can be repelled by a magnetic field?

Yes, there is a limit to the speed at which moving charges can be repelled by a magnetic field. This limit is the speed of light, which is approximately 299,792,458 meters per second. At speeds approaching the speed of light, the repelling force becomes weaker and eventually becomes zero. This is due to the effects of special relativity, which states that as an object approaches the speed of light, its mass increases, making it more difficult to accelerate it further.

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