Question

A magnet's magnetic fields is considered to be static. When the magnet is in motion does that mean B is no longer static?

Answer 1

Yes, but if the motion is not too fast, it is quasistatic, that means that the static equations remain valid at every instant.

Answer 2

Thanks

Answer 3

@Vincent-Lyon.Fr how fast must it be? So it cannot be considered static anymore...?!

Answer 4

@OneOwOne interesting topic!

Answer 5

It depends on the distance between source of field and point of action.

If the time of propagation of the EM wave along this distance is negligible compared to the time-period of the motion of the magnet.

Typically, if distance is 1 metre, then frequency of motion of the magnet must be less than \(3.10^8\text {Hz}\), typically 10 Mhz is ok on the scale of a lab table.

The actual max speed of the magnet will be given by above frequency and chosen amplitude of the oscillations.

Answer 6

@Vincent-Lyon.Fr If we think about it in a more general point of view... Most causes the magnet would be going at high speeds. In causes Im aware of where magnets are used, a magnet attracting another magnet or even repelling it, or the same is applied but with the use of an electromagnet... The magnet is moving very fast. So the magnetic field is certainly not static.

What do you think?

Answer 7

I thought the whole point of not being "Static" is the idea of motion, slow or fast I thought it didn't matter :P

Answer 8

I was not discussing "static", but "quasi-static", which is an approximation valid under certain conditions.
Of course, it applies also to changing fields of changing currents in electromagnets. The conditions on frequency and distance to the observer are the same.

Answer 9

yea I know @Vincent-Lyon.Fr ... I was saying that in most magnetic interactions between forces of repulsion or attraction of both magnets and electromagnets, the field is not static because the magnet or electromagnet is attracted/repelled pretty fast. Last post of mine was not written the way I intended it to :P

Answer 10

@Vincent-Lyon.Fr Um... I understood that it has to be fast.
But the point that relates "frequency" just got me lost.