Tag Archives: magnets

A Diamagnetic Demonstration


Our friends stopped by with a simple apparatus to demonstrate the diamagnetic properties of bismuth metal. Diamagnetism is a extremely weak magnetic effect — generally orders of magnitude weaker than everyday permanent magnets, which exhibit ferromagnetism. However it is also an extremely interesting effect because diamagnetic materials are repelled by magnetic fields. This is different than the case with ferromagnets, where one pole of a magnet repels another — rather, the entire material is (weakly) repelled by any magnetic pole.

Now, how might one observe such a weak effect? One way is to build a magnetic levitation rig, but the field configurations there are a little less obvious. With a simple but sensitive balance, we can see the repulsion directly. The balance above has a long wooden beam, a central pivot on two blocks of plastic, and a couple of coins on the far end for counterbalance.


At the business end of the scale, there is a cylinder of bismuth metal about 1 cm in diameter, held in place by a rubber band. We also have a larger rectangular block, which is our test magnet, made of grade N50 NdFeB and painted black. And finally, the Lego Astronaut Twins are here helping out as a scale and position reference.

Moving the block magnet beneath the bismuth, we can see what happens in an animated GIF:

After the balance settles, the resting position of the end with the bismuth is considerably higher. With some calibration in terms of weights and/or positions, one could even measure the exerted force with some precision.

A slight improvement to this apparatus would be to reverse the roles of the bismuth and the block magnet. That is, to affix the magnet to the arm of the balance, and to slide the bismuth beneath it instead. You could then use a nearby block of aluminum to damp the motion of the beam through magnetic (eddy current) damping. Many commercial balance-beam type scales already use magnetic damping so that they settle down to their final values faster.


Evil Mad Scientist Laboratories: Year 4

Impractical idea: Iron filing nail polish

spiky nail polish

Some time ago we came across a subtle magnetic nail polish. It had fine magnetic dust in it, and could record the local magnetic field profile at the time that the polish dried.

But hey, why can’t you do this with full-on iron filings? So, for our own bold and impractical take on this concept, we tried mixing genuine iron filings with nail polish (clear, in this case). Mix well, paint on, hold finger over (large) magnet while it dries. Don’t even think about trying to fit those spiky fingertips into gloves.

Results? So-so. The particles aligned with the field and solidified, but have more clumping than we’d like to see.

Maybe slightly finer particles would have been better. Much better would be if we found a good way to work with ferrofluid that could be hardened, or perhaps a version of magnetic viewing film that could be painted onto surfaces. Or maybe, if our version above were redone with RTV silicone, the particles could wiggle around in the presence of an external field.

We leave these important questions to higher minds than our own.

17 cool magnet tricks

Here are seventeen of our favorite magnet tricks, projects and demos.

Magnet tricks

Extract batteries from stubborn holders
We’ve all got things that take batteries. Some of them are well designed, and some of them are not. The worst offenders are electronic toys that take (say) half a dozen AA batteries, all of which must be inserted with the correct orientation– spring side first– and pried out, well, somehow. Rather than risk puncturing your batteries by prying them out with something pointy, just use a magnet to lift them out.
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The Hungry Scientist Handbook

 Today is the official release date for the Hungry Scientist Handbook, a new book by Patrick Buckley and Lily Binns.

The Hungry Scientist Handbook was conceived as a sort of cookbook for geek-centric food and– using the word a different way– as an a cookbook for food-oriented electronics– as evidenced by projects varying from polyhedral pies to LED lollipops.

We met Patrick and Lily at the 2006 Maker Faire, where they invited us to contribute a couple of chapters to their project. We did, and it’s finally out!

(We aren’t the only ones who are excited– we’ve seen write-ups at the LA Times and
Wired this week.)

A Computer Chip Trivet   Refrigerator magnetscrane crouton   12.  Fire!

We contributed a total of nine projects to the Hungry Scientist Handbook, some of which we have written about here. These include the Computer Chip Trivets, Crafty fridge magnets, Edible Origami, and (making a cameo appearance) the Lego Trebuchet.

Dry Ice Martini   Cold DrinkDry Ice Lemonade

We also contributed a few new cooking projects that involve dry ice: Dry (Ice) Martinis, Fizzy dry ice lemonade, and Dry ice root beer. (With Floating bubbles on CO2 as a bonus project.)

Smart Coasters   Smart Coasters

Smart Coasters

And… a brand new exclusive Evil Mad Scientist Laboratories electronics project that we developed just for the Hungry Scientist Handbook: Smart Coasters.
Smart Coasters are cast-plastic coasters for your drink that light up red when you put a hot drink on top and light up blue with a cold drink. The design is fully analog– no microcontrollers and no programming– and they incorporate a solar cell so that the whole thing is hermetically sealed: waterproof and washable. Complete step-by-step DIY instructions are included for both the electronics and the resin casting.

You can purchase the Hungry Scientist Handbook at booksellers including Amazon. Also visit their new web site, www.hungryscientist.com.

Making Crafty Fridge Magnets

Food comes in all kinds of shapes, sizes, and packages. Your kitchen cabinets, pantry drawers, and refrigerator shelves are already filled with marvelous little boxes and baggies of goodies. Some of these are cultural icons, others are silly modern wonders of neo-retro design.

You may even have your own little collection of interesting little containers in the form of left-over little boxes of candy from Halloween. What can you do with all these things?

Make them into an awesome array of fridge magnets!
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Super-Easy Supermagnet Compass

When I was a kid, I read in a science book about how to make a directional compass. You magnetize a sewing needle and balance it on a cork floating in a bowl of water. Even today, this is the standard story. For example, How Stuff Works still says that this is how to make a compass. (There are a lot of other examples, too.) It turns out that it’s a whole lot easier than that. All you need is a really good magnet.
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How to extract magnets from plastic toys

As Marty McFly says, “You don’t just walk into a store and buy plutonium.” Actually, all I was after was neodymium, but the principle still applies. I needed a pile of rare earth magnets in a hurry. Neodymium-iron-boron (NdFeB) magnets are cheap, extremely strong, and surprisingly ubiquitous. Despite this, most corner drugstores do not carry sets of rare-earth magnets, and it can be hard to get them unless you have a few days to wait for a package.

It turns out that you can get NdFeB magnets at the corner drugstore, and they’re cheap. You just have to extract them from the toys that they come in.
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