Why Does a Moving Charge Generate a Magnetic Field?

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    First law Law Maxwell
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Discussion Overview

The discussion centers around the question of why a moving charge generates a magnetic field, exploring the underlying principles of electromagnetism, particularly in relation to Maxwell's equations and the effects of relativity.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the fundamental reason behind the generation of a magnetic field by a moving charge, suggesting it may be a law without a clear explanation.
  • Another participant references Ampere's law and mentions that their professor described the phenomenon as a relativistic effect due to electrons moving at high speeds.
  • A participant elaborates on the relationship between electricity and magnetism, stating that they are fundamentally the same force, as described by Maxwell's equations, and that a Lorentz transformation of an electric field results in a magnetic field.
  • There is a clarification that a moving charge possesses both an electric field and a magnetic field, countering the implication that it might only have one or the other.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the electric and magnetic fields associated with a moving charge, with some suggesting a transformation between the two and others affirming the coexistence of both fields. The discussion remains unresolved regarding the deeper explanation of why a moving charge generates a magnetic field.

Contextual Notes

Some participants express uncertainty about the concepts of relativity and the transformations involved, indicating a potential limitation in understanding without complex equations.

Taturana
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I know that the first law of Maxwell states that every moving charge creates a magnetic field.

But, is there an explanation of WHY this happens?

Why a moving charge creates a magnetic field?

Or this is the kind of law that nobody knows why exist?

Thank you
 
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I assume you're referring to ampere's law. (generally Gauss's law is written as the "first" of Maxwell's equations.)

My physics professor told us it is actually a relativistic effect due to the electrons traveling near the speed of light. I found this thread which might elaborate on it more than I could.

https://www.physicsforums.com/showthread.php?t=175438
 
Ah that's the whole beauty of electricity and magnetism!

Turns out that Maxwell (the guy the equations are named after) discovered that electricity and magnetism are one and the same and that's why we now call the force the "electromagnetic" force.

Maxwell actually used 4 different laws, and collectively they are known today as Maxwell's laws. When Maxwell tried to combine the four equations he realized that they describe a wave that is a mixture of both electric and magnetic waves.

What this means is that electricity and magnetism are exactly the same. The reason a moving charge looks like it "creates" a magnetic field is because as stated by Nu naught has to do with relativity.

If you know anything about relativity you know about the Lorentz transformation. Well turns out that if you do a Lorentz transformation on a moving electric charge's electric field you get a magnetic field. This is due to the fact that moving things relativity to us appear to act differently according to the laws of relativity.

In summary electric and magnetic fields are one in the same. A moving charge "creates" a magnetic field by moving which is then subject to a Lorentz transformation which shows that all that happens is the electric field transforms into a magnetic field.
 
Feldoh said:
Ah that's the whole beauty of electricity and magnetism!

Turns out that Maxwell (the guy the equations are named after) discovered that electricity and magnetism are one and the same and that's why we now call the force the "electromagnetic" force.

Maxwell actually used 4 different laws, and collectively they are known today as Maxwell's laws. When Maxwell tried to combine the four equations he realized that they describe a wave that is a mixture of both electric and magnetic waves.

What this means is that electricity and magnetism are exactly the same. The reason a moving charge looks like it "creates" a magnetic field is because as stated by Nu naught has to do with relativity.

If you know anything about relativity you know about the Lorentz transformation. Well turns out that if you do a Lorentz transformation on a moving electric charge's electric field you get a magnetic field. This is due to the fact that moving things relativity to us appear to act differently according to the laws of relativity.

In summary electric and magnetic fields are one in the same. A moving charge "creates" a magnetic field by moving which is then subject to a Lorentz transformation which shows that all that happens is the electric field transforms into a magnetic field.

Thank you for the reply.

So, when a charge starts to move it's electric field is transformed into a magnetic field? So a moving charge has no electric field?

I'm not very good at relativity, but I have notions of the concepts. Is it possible to explain me without using complex equations what happens in relativity to the magnetic field to appear at a moving charge?
 
Taturana said:
So a moving charge has no electric field?

No, a moving charge has both an electric field and a magnetic field.
 

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