Physics of a Diamagnetic Hover Board [W/Video]James Lincoln
Small scale models which levitate diamagnetic materials such as this haven’t existed for the classroom, until now! It is only recently, with the creation of artificial neodymium magnets and artificial pyrolytic graphite, that the effects can finally be easily demonstrated.
Diamagnetism is a very interesting and promising phenomenon in which macroscopic objects can be made to float under their own influence. Both diamagnetism and paramagnetism remind us of the connection that exists between electricity and magnetism, and furthermore of the fact that all matter is made of moving electric charges. The Diamagnetic Levitator makes for a great classroom demo!
The arrangement of these strong magnets best demonstrates the diamagnetism of pyrolytic graphite.
A small wafe of “pyrolytic” graphite provides us with the best demonstration of “diamagnetic levitation.” To be “diamagnetic” means to always be repelled by a magnet.
Graphite is a molecule of carbon, an extended molecule that forms in flat crystal layers. But “Pyrolitic” graphite is when the crystal layers are much larger, and include several covalent bonds between the layers, as they are grown very slowly in a vacuum at high temperature.
The ball & stick model (author’s conception) of the graphite molecule (hexagonal crystal).
Regular graphite, like pencil lead or anthracite coal, is diamagnetic too, but in the case of pyrolytic graphite, the effect is 25 times stronger. This makes pyrolytic graphite the strongest diamagnetic substance by weight.
Several other substances are also diamagnetic, such as sulfur, bismuth, and glass. These will always be repelled by a magnet. But very, very, weakly. Therefore, we almost never notice the effects of diamagnetism. It is only now with artificial neodymium magnets and artificial pyrolytic graphite that the effects can be so easily demonstrated in our classrooms.
A piece of bismuth, resting on a Styrofoam boat, is pushed slowly by a very strong magnet’s field. This demonstration also works with a large piece of sulfur or a small test tube of water – but not as well.
Some teacher (or textbook) probably even told you that ONLY iron and a few other metals experience magnetism. That is simply not true, every substance has some magnetic properties. This is because magnetism is caused by moving electric charges and every substance contains moving electrons. When there is an overall repulsion, we call the substance diamagnetic.
Sometimes there is weak overall magnetic attraction we call that case paramagnetic. This is the case with many substances, but especially with liquid oxygen, aluminum, and tungsten.
Lastly, but most familiarly, when the object itself becomes a magnet for an extended period of time, we call that situation ferromagnetism. This is named for iron of course, although there are some other ferromagnetic substances such as like cobalt, nickel, and alloys of neodymium.
Perhaps most interesting, water is diamagnetic, and can be repelled by magnets. No one would have ever guessed. This is interesting not just because it is a surprise, but because the application can be to floating living creatures in magnetic fields. Yes. You are next!
A frog floats, unawares, in an extremely strong magnetic field, thanks to the diamagnetism of water.
A similar effect is achieved with the graphite which makes for an excellent hands-on demo.
In conclusion, most teachers and students are unaware of the interesting and varied effects of diamagnetism. This is unfortunate because it is a very interesting and promising phenomenon in which macroscopic objects can be made to float under their own influence. Diamagnetism and paramagnetism remind us of the connection that exists between electricity and magnetism, and furthermore of the fact that all matter is made of moving electric charges. The reality of these effects nearly completely canceled out, except when careful observation is applied. Learn more about the Diamagnetic Levitator.
James Lincoln is an experienced physics teacher with graduate degrees in education and applied physics. He has become known nationally as a physics education expert specializing in original demonstrations, the history of physics, and innovative hands-on instruction.
The American Association of Physics Teachers and the Brown Foundation have funded his prior physics film series and SCAAPT’s New Physics Teacher Workshops.
Lincoln currently serves as the Chair of AAPT’s Committee on Apparatus and has served as President of the Southern California Chapter of the AAPT, as a member of the California State Advisory for the Next Generation Science Standards, and as an AP Physics Exam Reader. He has also produced Videos Series for UCLA’s Physics Demos Project, Arbor Scientific, eHow.com, About.com, and edX.org.