Question about electromagnetism and frames of reference

In summary, the discussion involves how electromagnetism behaves differently depending on the observer's frame of reference, particularly in the context of special relativity. It highlights the concept that electric and magnetic fields can transform into one another when switching between moving and stationary frames, leading to the conclusion that forces acting on charged particles depend on the observer's relative motion. This interplay challenges classical notions of simultaneity and emphasizes the importance of understanding electromagnetic phenomena within the correct frame of reference.
  • #1
abdossamad2003
68
4
in this text:
1.jpg


my question is in highlighted line:
"The two rods have the same length (in S) and contain the
same number of charges." why?

Considering that the negative rod has movement, it should have a shorter length than the positive rod according to a relativity!
 
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  • #2
abdossamad2003 said:
in this text:
View attachment 340896

my question is in highlighted line:
"The two rods have the same length (in S) and contain the
same number of charges." why?

Considering that the negative rod has movement, it should have a shorter length than the positive rod according to a relativity!
There was a long thread about this recently. If you set up a steady current in an infinite length of wire, then it's not clear whether the moving charges get closer together or not. It all depends on how you accelerate them.

If, however you consider a physically realistic large rectangular loop of wire, then the moving charges must have the same charge density, as no charges gave been added or taken away from the wire. This is in the rest frame of the wire.

This means that in the rest frame of the moving charges in a section of the wire, the charges must have got further apart. And the stationary charges will be closer together in this frame.

Note that there is no single rest frame of the moving charges throughout the whole loop.
 
  • #3
 
  • #4
abdossamad2003 said:
my question is in highlighted line:
"The two rods have the same length (in S) and contain the
same number of charges." why?

Considering that the negative rod has movement, it should have a shorter length than the positive rod according to a relativity!
The authors of this book assume, that the rest length of the rod, which is moving in frame ##S##, is greater than the rest length of the other rod at rest in frame ##S##.

"It is a well-known fact that a current-carrying wire is neutral ... in the lab frame", and therefore a positive surface charge density must compensate the negative volume charge density, according to
http://web.mit.edu/wangfire/misc/AJP000360.pdf
 
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FAQ: Question about electromagnetism and frames of reference

What is electromagnetism?

Electromagnetism is a branch of physics that deals with the study of electric and magnetic fields and their interactions with matter and with each other. It encompasses phenomena such as electric currents, magnetic fields, electromagnetic waves, and the forces between charged particles.

How do frames of reference affect observations in electromagnetism?

Frames of reference significantly affect observations in electromagnetism. According to the theory of relativity, the observed electric and magnetic fields can change depending on the observer's frame of reference. For instance, a moving observer may perceive a magnetic field where a stationary observer sees only an electric field, and vice versa.

What is the relationship between electric and magnetic fields in different frames of reference?

The relationship between electric and magnetic fields in different frames of reference is described by the Lorentz transformation equations. These equations show how the components of the electric and magnetic fields transform when switching from one inertial frame to another, ensuring that the laws of electromagnetism are consistent with the principles of special relativity.

Can you explain the concept of electromagnetic waves in the context of frames of reference?

Electromagnetic waves, such as light, consist of oscillating electric and magnetic fields that propagate through space. In different frames of reference, the frequency and wavelength of these waves can change due to the Doppler effect, but the speed of light remains constant in all inertial frames, as dictated by the theory of relativity.

How does the theory of relativity integrate with electromagnetism?

The theory of relativity integrates with electromagnetism through the unification of electric and magnetic fields into a single entity known as the electromagnetic field tensor. This tensor formalism ensures that Maxwell's equations, which govern electromagnetism, hold true in all inertial frames of reference, thereby aligning with the principles of special relativity.

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