Magnetic force -- does it fall off to zero far away from the source?

Join the discussion
Ask a follow-up here, or get your own question answered by working scientists, mathematicians and engineers — people, not an autocomplete.
Real named experts · corrections over time · the nuance an AI answer skips
Sign up Log in
7 replies · 2K views
Yahya Sharif
Messages
39
Reaction score
4
Let's say we have a wire and a circuit is closed the magnetic field start to spread with speed of light c. Then we would have a place " out of range " at which the magnetic field doesn't exist.What is the equation that connects magnetic force with distance with its prorogation of speed of light c and with its range ?
 
Physics news on Phys.org
Yahya Sharif said:
Let's say we have a wire and a circuit is closed the magnetic field start to spread with speed of light c.
Actually, it'll be an electromagnetic field, not a pure magnetic field.

You need to look up the Lienard-Wiechert potentials, which describe fields from general moving charges. The maths is not simple, I'm afraid.
 
  • Like
Likes   Reactions: vanhees71
Ibix said:
Actually, it'll be an electromagnetic field, not a pure magnetic field.

You need to look up the Lienard-Wiechert potentials, which describe fields from general moving charges. The maths is not simple, I'm afraid.
haha I am in physics II right now and this totally blew my mind. We just learned about Maxwell's equations and now I learned they have some sort of contradiction and they still don't describe everything. Thanks
 
khamo said:
We just learned about Maxwell's equations and now I learned they have some sort of contradiction and they still don't describe everything.
I'm afraid I don't understand this comment. There are no contradictions that I'm aware of, and the only thing Maxwell's equations don't cover in electromagnetism is quantum theory.

Edit: The Lienard-Wiechert potentials, if that's what you are referring to with "don't describe everything", are a solution to Maxwell's equations for a particular scenario.
 
Last edited:
Ibix said:
I'm afraid I don't understand this comment. There are no contradictions that I'm aware of, and the only thing Maxwell's equations don't cover in electromagnetism is quantum theory.

Edit: The Lienard-Wiechert potentials, if that's what you are referring to with "don't describe everything", are a solution to Maxwell's equations for a particular scenario.

ok i wasn't sure to the inclusivity about the Lienard-Wiechert potentials but I was referring to how in the article it talks about how there's a problem with maxwell's equations and linearity?
 
khamo said:
We just learned about Maxwell's equations and now I learned they have some sort of contradiction and they still don't describe everything.
Guessing at the meaning...

Maxwell's equations by themselves are self-consistent. No contradictions. But if you add the principle of relativity (the laws of physics are unchanged regardless of the choice of inertial reference frame) and if you try to transform measurements between frames using the Galilean transforms then contradictions emerge.

One way out is to hypothesize a medium against which electromagnetism operates -- the ether. Another way out is to use the Lorentz transform and discard the notion of absolute time. The result is Special Relativity.

Maxwell's equations do not describe everything. They do not describe gravity, the strong nuclear interaction, or the photoelectric effect.
 
jbriggs444 said:
Guessing at the meaning...

Maxwell's equations by themselves are self-consistent. No contradictions. But if you add the principle of relativity (the laws of physics are unchanged regardless of the choice of inertial reference frame) and if you try to transform measurements between frames using the Galilean transforms then contradictions emerge.

One way out is to hypothesize a medium against which electromagnetism operates -- the ether. Another way out is to use the Lorentz transform and discard the notion of absolute time. The result is Special Relativity.

Maxwell's equations do not describe everything. They do not describe gravity, the strong nuclear interaction, or the photoelectric effect.
Right i guess that was the general point i was alluding to.

I actually misinterpreted what i was reading. What i meant to say was that 'linearity of Maxwell's equations in vacuum allows one to add both systems, so that the charges disappear'.

which is kind of like a contradiction? what are the 'systems' they are talking about?