Repeated the magnetic levitation of pencil carbon that was shown on youtube.

SWEET!

This, I gotta try. First super-magnet and pencil graphite didn't show much of an effect, gotta rummage through the drawers for a bit...

An easier demo of diamagnetism is with a Ziploc bag of water ducktaped to a long string (fishline works well). Hang it from the ceiling, and move a magnet along the floor, you can easily see the deflection. Don't need an especially strong magnet.

You want pyrolytic graphite for the best effect. I have a sheet of it floating above four gold-plated NdFeB magnets over my workbench. I bought it off the Web some years ago. The more physics somebody knows, the bigger the double-take. (It looks exactly like the Meissner effect--I have a routine about having discovered a room-temperature superconductor but having no particular use for one, I just made a demo....)

Cheers

Phil Hobbs

On a sunny day (Fri, 01 Jul 2011 18:16:29 -0400) it happened Phil Hobbs wrote in :

LOL investors money!

On a sunny day (Fri, 1 Jul 2011 13:58:24 -0700 (PDT)) it happened whit3rd wrote in :

It is easy to test if the leads are made of the right stuff: Put one on a flat table, if you can push it forward without touching with a N or S pole of a strong permanent magnet, then it should be able to do the levitation thing too.

Care to post a photo?

Sure, if I haven't packed it yet--I don't remember. The movers are coming tomorrow, so it's a bit chaotic round here.

Cheers

Phil Hobbs

How about some photos of your new office & lab, when you get a chance? :)

Definitely. It's a bit over 1k square feet, so there'll be a lot of empty space initially!

Cheers

Phil Hobbs

Okay, the fake Meissner demo for your delectation.

Some stills, showing daylight under the graphite sheet:

And a movie:

I really have to go back to packing boxes now.

Cheers

Phil Hobbs

I assume that the multipe magnets make a sort of bowl-shaped field, so the graphite doesn't slide off the top.

What I don't understand is the case where a chunk of high-temp superconductor sits on a single magnet, and LN2 is poured on, and it lifts straight up. I've seen it done. It doesn't slide off to one side, so it's pinned somehow.

There was some guy who used to post here that swore that Earnshaw's theorem made stable suspension impossible, and that all the pictures like yours were faked. Walz?

John

Earnshaws Th does not apply to diamagnetic materials, nor spinning ones. Thanks for the pics - quite impressive!

I knew that! But I still don't understand the lateral stability.

I think you can do stable suspension with AC fields levitating a conductive sphere or sheet. That should make more impressive distances.

John

Neat! :-) Thanks for posting those.

Ed

The field is a quadrupole, so there's a minimum of |B| in the middle, which is what provides the self-centring.

I'd have to think about how the Meissner effect makes the magnet stable--probably only works with Type 2 superconductors, where you get magnetic vortices, so that the material is frozen to the field like as in the solar photosphere.

Cheers

Phil Hobbs

Cheers

Phil Hobbs

On a sunny day (Wed, 06 Jul 2011 13:17:50 -0400) it happened Phil Hobbs wrote in :

Nice!

Yes with the pencil lead you also get that typical wild movement in 3 D if you touch it. One thing I contemplated was to file a flat side on the pencil lead, blow some air over it so it rotates, and shine my laser-pen against it, That would create one scan line. Then to add an electromagnet to push one side of the rod up / down (modulate the magnetic field in that area), and that would give a low scan teevee.

You can perhaps sync in H with a simple photo-diode that gets hit every rotation. Video modulating the laser pen from a DAC in an FPGA perhaps. But first back of the envelope calculations show a too low scan rate and to much instability to make a laser projector. Laser projectors go for a few hundred dollars these days, in color too.

I think you could modulate the position of that piece in your setup too, dunno how fast though (air resistance, mass). Coat it with some reflective material. Rotation of a pencil lead should be possible at high speed however.

It is just one of the 'out there' experiments I sometimes dream up. Just lucky it did not trigger Andreas Fault.

On a sunny day (Wed, 06 Jul 2011 18:05:27 -0700) it happened John Larkin wrote in :

This refers to impurities in the superconductor as a cause:

True, but the material tends to heat up. Suspending a magnet over field coils is possible with active circuitry and feedback.

If a type 1 superconductor is chilled while sitting on a magnet, it will repel (and rise). A type II, on the other hand, will pin the flux, so if it's chilled outside a magnetic field, it repels, but if it's chilled in a magnet field, it becomes an electromagnet...

Ferromagnetic items can only be attracted to a field maximum, which cannot (for B fields) exist in free space. So, you can't make soft iron into a stable floater, unless you use dynamic control fields (Jesse Wakefield Beams-style).