# Can a Rotating Magnet Prove the Relativity of Electric Fields?

• pmb
In summary, the conversation discussed a web page about a rotating magnet and its relation to the relativity of electric fields. The concept of charge density variation and its connection to superconductivity was also mentioned, along with a model called "big wave, little wave." The relevance of the Feynman lectures to understanding these concepts was brought up and the legitimacy of treating charge density in the same way as charge in QFT was questioned.
pmb
[SOLVED] Rotating Magnet

I had forgotten about a web page I made several months ago. It's regarding a rotating magnet. There are some cool physics in this page so take a look

www.geocities.com/physics_world/em/rotating_magnet.htm

Back in the early 60's Edward Purcell came out with an idea of how to look at the relativity of electric fields in terms of charge densities. It's not a widely know fact but under some circumstances you can have a zero charge density in one frame of referance and a non-zero charge density in another. If you want to go into the excrutiaing detail the see also

"Magnetism, Radiaton, and Relativity," Daniel V. Schroeder, Weber
State University --physics.weber.edu/schroeder/mrr/MRRnotes.pdf

Pete

An interesting page you have there.

I found out about the charge density variation when I was trying to understand superconductivity. It led to a model I call "big wave, little wave" where the big wave is the charge variation across the loop when it is turning and the little waves are the variations which couple the electron pairs to the vibrations of the crystal lattice.

Originally posted by Tyger
I found out about the charge density variation when I was trying to understand superconductivity. It led to a model I call "big wave, little wave" where the big wave is the charge variation across the loop when it is turning and the little waves are the variations which couple the electron pairs to the vibrations of the crystal lattice.

If you're interested in the details see the Feynman lectures. If youd don't have them then I put the relevant section online

http://www.geocities.com/physics_world/feynman-1.jpg
http://www.geocities.com/physics_world/feynman-2.jpg
http://www.geocities.com/physics_world/feynman-3.jpg
http://www.geocities.com/physics_world/feynman-4.jpg
http://www.geocities.com/physics_world/feynman-5.jpg
http://www.geocities.com/physics_world/feynman-6.jpg

Pete

I've got the Feynman Lectures

and would highly reccomend them to anyone who's serious about learning Physics. And they're a joy to read and study, he makes the ideas come alive. And the "big wave" idea came right out of Feynman, but I added the little waves to understand the Cooper Pair couplings in SC.

In a somewhat related question, I've always wondered about the legitimacy of treating charge density on the same footing as charge in QFT. Is it really rigorous?

## 1. Can a rotating magnet demonstrate the existence of electric fields?

Yes, a rotating magnet can demonstrate the existence of electric fields. When a magnet rotates, it creates a changing magnetic field, which in turn induces an electric field. This phenomenon is known as electromagnetic induction and is one of the fundamental principles of electromagnetism.

## 2. How does a rotating magnet prove the relativity of electric fields?

A rotating magnet demonstrates the relativity of electric fields by showing that the strength and direction of the induced electric field depends on the relative motion between the magnet and the observer. This is consistent with the principles of relativity, which state that physical laws should be the same for all observers in uniform motion.

## 3. Is a rotating magnet a reliable way to demonstrate the relativity of electric fields?

Yes, a rotating magnet is a reliable way to demonstrate the relativity of electric fields. This phenomenon has been extensively studied and tested, and it is consistent with the principles of electromagnetism and relativity. Additionally, it can be easily replicated in experiments and observed in everyday devices such as generators and motors.

## 4. Can a rotating magnet prove the existence of both electric and magnetic fields?

Yes, a rotating magnet can prove the existence of both electric and magnetic fields. As mentioned before, a rotating magnet creates a changing magnetic field, which in turn induces an electric field. This demonstrates the interconnected nature of these two fields, as described by Maxwell's equations.

## 5. Are there any other ways to prove the relativity of electric fields?

Yes, there are other ways to prove the relativity of electric fields. One example is the use of a moving charged particle in a magnetic field. This also demonstrates the interdependence of electric and magnetic fields and their behavior in different reference frames.

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