Would a vibrating bar magnet produce an oscillation in the magnetic field?

Question

An oscillating electric charge produces an oscillating electromagnetic wave. What if I were to shake a bar magnet violently ? Would it also produce an oscillating electromagnetic wave or does this just change the magnetic field ?

Voting to reopen. I have edited the question to make it clearer, although i think it was pretty clear in the first place. — gandalf61, Dec 23 '23 at 16:13

score 2 · Answer 1 · answered Dec 23 '23 at 21:51

Yes, it would produce an oscillating electromagnetic wave.

It is interesting to compare with the situation of a changing magnetic field by the effect of a magnet travelling at constant velocity. At any point outside it, the Maxwell equations without sources applies. And as a consequence, the wave equation:$$\frac{\partial^2 B_j}{\partial t^2} = c^2\nabla^2 B_j$$ also applies for any $j$ component of the magnetic field. However the solution of that wave differential equation is not an electromagnetic wave in this case. It is not a function of the form $B_j = A_1f(\mathbf {k\cdot r}-\omega t) + A_2f(\mathbf {k\cdot r}+\omega t)$.

It is necessary an accelerated magnet to get it.

score 1 · Answer 2 · answered Dec 23 '23 at 15:08

1

An oscillating or turning bar magnet induces an electric field, one uses a rotating bar magnet in a dynamo, there are even dynamos where you have just to shake a magnet up and down.

answered Dec 23 '23 at 15:08

trula

6,146

score 1 · Answer 3 · answered Dec 23 '23 at 15:15

Here is a posts about the kink in the field and why it appears. See the links in it too. Why does the kink has the following vector direction?

Physics is a description of the behavior of the universe. There is more than one way to describe it. In one description, E and B fields are two separate related fields. In another, they are pieces of a single more complex field.

The first way is how the fields were understood historically. This is still in common use today because it is easier to understand and use for everyday problems. The second makes more sense in the light of special relativity.

Moving a magnet creates a kink in the magnetic field. This spreads outward. A changing magnetic field induces a changing electric field. A changing electric field induces a changing magnetic field. These changes spread out at the speed of light. This is an electromagnetic wave. So a moving kink is the same as an electromagnetic wave.

Note that you produce waves with a very very long wavelength by shaking a magnet. Suppose you shake it back and forth once per second. You produce a wave with a frequency of 1 oscillation per second. By the time you have finished an oscillation, the part of the wave from the start is 186,000 miles away.

score -1 · Answer 4 · answered Dec 26 '23 at 05:16

An oscillating electric charge produces an oscillating electromagnetic wave.

An electron on the surface of a conductor that is accelerated by an electric field emits photons. An electron in a particle accelerator as well as the electron in a free-electron laser emit photons during their magnet-induced deflection from the straight path. It can be assumed that the electrons on the surface of a magnet that is moved back and forth mechanically also emit photons.

What if I were to shake a bar magnet violently ? Would it also produce an oscillating electromagnetic wave or does this just change the magnetic field ?

An EM wave is a measurable object. The photons in such a wave are polarised and their electric and magnetic field components periodically change their sign. Such EM waves are generated by wave generators for radio sources. In contrast, EM radiation - originating from a thermal source, i.e. everything that surrounds us - is a non-polarised stream of photons. If I now shake a magnet, three phenomena can be recognised on the measuring detector

the quantity of thermal photons (i.e. the thermal radiation) fluctuates depending on the movement towards or away from the detector, whereby this phenomenon probably requires a thermally insulated observation cell in order to suppress the background noise from other thermal sources
the mechanical acceleration of the electrons on the surface of the magnet leads to the emission of photons, which can then leave the magnet (the emission inside the magnet is immediately absorbed again and thermal radiation is ultimately produced)
the movement of the surface electrons in the magnetic field of the magnet should lead to Hall effects or the Lorentz force, i.e. cause a charge displacement. Photons are also emitted during these accelerations.

Would a vibrating bar magnet produce an oscillation in the magnetic field?

The magnet will emit EM radiation with periodic intensity fluctuations.

Would a vibrating bar magnet produce an oscillation in the magnetic field?

4 Answers4