Eddy currents

Yes.

A fun demonstration is to drop a super-magnet down a piece of copper pipe. Try it sometime.

Clifford Heath.

yes..

In fact, letting a penny slide down an inclined plane, and then pass thru a magnetic field, is an EXCELLENT way to determine if it is a real (1982 or earlier; will drop out fast) or if it is one of the modern US Counterfeit (zinc laminates; shoots out almost straight).

Some scales use a permanent magnet and a flat piece of copper to damp out oscillations

Dan.

As in all things science, the meaningful answer depends upon the parameters. In this case, the strength of the current and subsequent losses depend upon the magnet's strength, its speed, the copper's dimensions, and especially the distance between them.

You might say that every moving magnet in the universe is inducing current in every piece of copper in the universe, except that there must be a quantum limit. It must have something to do with the state of the electrons in the copper. Does anyone know how moving magnetic fields move electrons and why there is a minimum field strength and velocity? As simply as possible.

Thanks, Bob

move electrons and why

There isn't. How's that for simple? ;)

Momentum and energy aren't quantized for free particles.

Since the free particle states form a continuum, there's always an empty state available, regardless of how large or small the kick.

Cheers

Phil Hobbs

I don't think there is any quantum limit. At very low fields the motion caused by weak fields is swamped by the thermal motion of the electrons. (There is the magnetic flux quantum in super conductors....

George H.

Photons.

There's not but it's a inverse-square law in speed and strength in distance it's inverse 4th power (I think).

AFAIK, the flux quantum has been detected in small, cool, resistive loops as well.

Tim

Right, you don't need a super conductor. Just a loop. There's the Aharonov-Bohm effect.

I think there have been shifts seen in electron transport, where there is some scattering path where the electron can make a loop.. All at low temperature, the electron has to scatter without losing energy(?) or at least phase information.

At some deep level flux quantization relates to charge conservation. (QM gets weird.. cue Dirac)

George H.

Yes, that's probably right. I was designing a swinging pendulum with a permanent magnet on the bottom of the pendulum swinging by a coil of wire which triggered a circuit that applied the battery voltage to the coil for a short pulse to give it a push and keep it going. I was winding my own coils and found that using fiberglass for the coil form worked better than using copper PCB board. I got tired of cutting out the discs for the coil form and found that a ordinary Quarter (currency type) was just the right size. So, I tried a couple copper quarters for the top and bottom pieces of the coil form and it failed. I had to use twice the voltage to keep the pendumlum swinging indicating heavy losses.

. .

And the speed of light limit.

How can I get in touch with Eddy? I'd like to buy a few dozen currants.

What is a currant? Some sort of ant species?

A little raisin?

you got two problems there: the quarters will absorb some of the pulse reducing the amplitide of the external magnetic field of the coil. Also the quarters will cause drag on the moving magnet.

use fibre or nylon washers as end forms (or just buy an inductor).

A crossbred (cur) ant perhaps.

:)

There's red currants and black currants....

Does the colour signify polarity?

Yes, red ants are positive about biting you.

NT