Fun With Magnets


Adam Beehler

In each newsletter, Adam Beehler, Lecture Demonstration Specialist, explains one of his demonstrations. Adam recently authored two articles, published in The Physics Teacher:
•“Demonstrating the photoelectric effect using household items” (Vol. 48, 348. 2010) •“Demonstrating spectral band absorption with a neodymium light bulb” (Vol. 48, 206. 2010)

 

If you have ever played with magnets, then you know that they attract iron (or steel, which contains iron). Iron is one of the most common ferromagnetic materials. Most people are aware of this and delight in having various objects “stick” to magnets. Just think of all the objects we use every day that involve magnets. I would like to feature two objects that are not normally thought about as magnetic – paper currency and Total cereal.

The United States Treasury uses “magnetic ink” to print its currency. Magnetic ink is basically just printer ink toner with iron oxide particles mixed into it. This is just one of the many counterfeiting defenses in place. Granted, we usually do not notice or think of our paper money as being magnetic; however, with a strong magnet (like a neodymium iron boron magnet) you too can verify this at home. Dangle a bill or flop it on a table and bring your strong magnet right up against an area on the bill with a lot of ink. You should see the bill slightly attract to the magnet. You will not get the same reaction as when you bring a magnet near an iron nail, but you will nonetheless verify that our money does indeed contain iron. If you fold and tape a bill so that the ink sections are all together, then your magnet might even hold it up.

Total cereal claims it provides 100% of our recommended daily allowance of iron. Did you ever wonder how much that is or what this iron looks like in our cereal? Well, now’s your chance! All that iron makes the flakes magnetic. Here are a few ways to verify this. Sufficiently crush up many flakes and rub your strong magnet around in the crumbs. After removing the magnet, you should see tiny bits “stuck” to it. This is due to the iron in the cereal. But maybe you are thinking, “Ah, this is just attracting due to electrostatic forces.” Well, do it again and convince yourself. Or better yet, float some flakes on the surface of water and bring a strong magnet very near one of those flakes. You should see the flake attract to the magnet. As you slowly move the magnet around, the flake should follow you (until it gets too soggy and sinks). Try attracting different sized flakes.

Of course my favorite thing to do with Total cereal is to make a slurry out of it and pull those tiny little pieces of iron right out of the cereal. One easy way to do this is to use a blender to mix, say, a cup or two of cereal with a cup or two of warm water (warm, so that it will not take as long to mix). Mix for awhile, but then wait many minutes for the water to soak into the cereal, then keep mixing some more. This will result in a much finer slurry. I put the slurry in a re-sealable bag and very slowly slide my strong magnet around the outside of the bag. While the magnet is pressing into the bag, any free iron particles should slowly move to the magnet. If you are careful not to come out of contact with the bag, then you can accumulate more and more iron as you slowly slide around. When you think you have enough, slowly slide the magnet up out of the slurry so that you can see the iron. Pretty cool, huh?! (Before you ask, yes, this is safe to digest.) Try investigating other cereals and foods, and have fun with magnets!

You can also view this demo, and a complete materials list, here.