Eddy currents

If a permanent magnet passes by a flat piece of copper the size of a quarter (currency) , are there any eddy currents induced and I^2 losses occurring ?

Reply to
billbowden
Loading thread data ...

Yes.

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

Clifford Heath.

Reply to
Clifford Heath

yes..

Reply to
Robert Baer

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).

Reply to
Robert Baer

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

Dan.

Reply to
dcaster

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

Reply to
Bob Engelhardt

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

Reply to
pcdhobbs

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....

formatting link
I don't think that applies to non-super conductors, but I could be wrong.)

George H.

Reply to
George Herold

Photons.

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

formatting link

--
This email has not been checked by half-arsed antivirus software
Reply to
Jasen Betts

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

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
 Click to see the full signature
Reply to
Tim Williams

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

formatting link

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.

Reply to
George Herold

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.

. .

Reply to
billbowden

And the speed of light limit.

--
John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
 Click to see the full signature
Reply to
John Larkin

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

Reply to
John S

What is a currant? Some sort of ant species?

Reply to
billbowden

A little raisin?

Reply to
krw

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).

--
This email has not been checked by half-arsed antivirus software
Reply to
Jasen Betts

!

A crossbred (cur) ant perhaps.

:)

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

Does the colour signify polarity?

--
This email has not been checked by half-arsed antivirus software
Reply to
Jasen Betts

Yes, red ants are positive about biting you.

NT

Reply to
tabbypurr

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.