As we discussed on our diamagnetism main page, water is diamagnetic, though about 20 times less than Carbon-Graphite or Bismuth. When exposed to a magnetic field, it produces a weak magnetic field in the opposite direction. Also, this means it is repelled by a magnetic field. This page shows some simple experiments that demonstrate the diamagnetic properties of water.
One of our goals up here at Wondermagnet Laboratories is to get a tiny drop of water to levitate above four permanent magnets. It's probably not possible with currently available grades of magnet, but as N-I-B magnets improve in quality, it may be possible soon. Scientists at the University of Nijmegen (Holland) high-power magnet labs successfully levitated a small frog over a very powerful superconducting electromagnet...it worked because of the diamagnetic properties of water, protein and DNA in the frog's body.
Experiment 1 -- Oil Drops and Water
Fill a small glass jar 2/3 full with rubbing alcohol. Add a couple drops of vegetable oil, which will fall to the bottom of the jar. Add water a little bit at a time, gently swirling the jar, until the specific gravity has been adjusted so that the oil drops neither float nor sink--they will be suspended in the middle.
Add a bunch more tiny oil droplets, set on a countertop, and place a large N-I-B magnet or stack of magnets next to the jar. The stronger the magnet, the faster the droplets move. We used our Item #37, one of the largest, most powerful N-I-B magnets available--but stacks of smaller magnets will work in this experiment also. You should be able to see the oil droplets slowly migrating toward the strong magnet. After a few minutes, they will collect around the pole of the magnet:
The magnet is repelling the water in the mixture, causing the oil droplets to collect at the area of strongest magnetic field.
Experiment 2 -- Magnet Bends Water Surface
This experiment gives a very subtle result that can be hard to see. When it can be made visible, it's quite dramatic. We've tried to come up with ideas for better visibility that allow this experiment to be performed as a classroom demonstration. Please let us know if you have any ideas about this!
Place the strongest N-I-B magnet you can find at the bottom of a shallow tray or petri dish. Fill with water so the magnet is just barely covered. You'll have to cover it enough so that it's obvious that the force at work is NOT surface tension--1/8 to 1/16 of an inch covering the magnet is ample. If there are real skeptics in your audience, put only an 1/8 to 1/4 inch of water in the petri dish, and place the strong magnet UNDERNEATH the dish--the effect still works, proving that surface tension is not causing it. Perform this experiment on a sturdy surface like a workbench or countertop, as vibrations will cause enough ripples that the effect won't be visible. We used our Item #11 for these photos.
The visible effect is a depression in the water's surface over the pole of the magnet. The magnet is repelling the diamagnetic water, pushing it off to the sides. It's a subtle effect, so try these tips for demonstrating it:
Distortion of light beam reflection from magnet.
Hang an icicle from a piece of thin fishing line. Tie it so the icicle is balanced--you can also cast a piece of ice in the freezer that is a long cylinder to make it easier to balance. Bring a strong N-I-B magnet or stack of magnets toward one end of the icicle, and it will spin slowly away from the magnets. We tried it with an ice cube without success--the longer lever arm of the icicle makes it possible. Also, we tried it with thread instead of fishing line, and the twist in the thread trying to unravel made the icicle spin hard enough that the diamagnetic repulsion could not overcome it.