# Spinning magnet in space and EM waves but how?

If we take an iron disc in space that is spinning on its axis, no electron in sight for miles other than the disc. The disc is magnetized with 2 poles. Speaking from an electrical potential, yes the dipoles are all lined up in one direction in the disc but the potential difference from one side to the other I think is fair to say is completely negligible. The magnetic field travels out into infinity at the speed of light and any change that happens to it also travels out. If the sun suddenly disappeared I think we can all agree that the earth continues to orbit around the location for another 8 minutes or so. In the same way the magnetic field extends out. What we are really looking at is the changing magnetic field from this disc as it radiates outwards. Ok let's up the receiving side, a ferrite core with a coil around it, just like an AM radio. Will it be able to pick up "the signal" and is this signal an electromagnetic wave, and if yes, is there a varying electric field that exists between the receiving antenna and spinning magnet, and if yes, where does this come from?

• Comment on your overall series of questions: I think you're looking for the EM field to be a disturbance in a sea of electrons, like ocean waves, or like sound is a disturbance in the atmosphere — but it's not. The field is the field. The field doesn't depend on any more fundamental thing (that we've discovered). Charged particles are just along for the ride, getting pulled around by the field and tugging on it in return. Oct 12, 2021 at 16:11
• Actually I'm trying to not think of electrons, I'm looking at the field in space. Of course it would tug on electrons, no doubt about that. I love your statement "the field is the field" that is very confidence inspiring. Oct 12, 2021 at 16:22
• While I love your question, I'm not sure this is the best stack for it. Have you considered migrating this to the Physics stack? This is probably why it has received downvotes
– David Hoelzer
Oct 13, 2021 at 14:47
• @DavidHoelzer I think you are 100% correct. Oct 14, 2021 at 13:17
• In that case, let's see if we can migrate this. :)
– David Hoelzer
Oct 14, 2021 at 14:14

Will it be able to pick up "the signal"

Yes (under ideal conditions, at least; obviously this isn't a practical experiment; a magnet spinning at a practical speed would be a very weak radiator, the wavelength would be very long, the far field region would be very far away, etc.).

and is this signal an electromagnetic wave

Yes.

and if yes, is there a varying electric field that exists between the receiving antenna and spinning magnet

Yes.

and if yes, where does this come from?

From the self-interaction of the electric and magnetic components of the electromagnetic field. Any spatial variation in the electric component causes a change in the magnetic component, and any spatial variation in the magnetic component causes a change in the electric component. In the equilibrium (that is, when we're far enough away from any phenomena that disturb one component or the other), this settles down to a propagating EM wave with the two components in phase and the ratio between them being 377 ohms.

• Comments are not for extended discussion; this conversation has been moved to chat. Oct 13, 2021 at 13:32

Feeling smart, might delete this later, idk.

We don't know "how."

We do have a model that we use to try to describe and predict interactions like the one you describe. EM waves or particles will indeed travel to your described receiver for detection... or more accurately, that's what happens in our model.

This is an incredibly unsatisfying answer, sorry. :-(

BTW, you should consider spending some quality time over at the Physics SE to see if this Q has been A'd over there, and ask it yourself if not!

• We don't know "how." is the best answer I've heard all week actually. Oct 12, 2021 at 13:28