Marvelous Interactions between Metallic Money and Magnets

National Chemistry Week (NCW) is only a little over a month away! It will be held October 20-26, and this year’s theme is Marvelous Metals! I always try to find some time to explore experiments and demonstrations that relate to upcoming NCW themes,^1-4 and this year has been no different. For this year’s theme, I found some inspiration from Andres Tretiakov’s article on detecting nickel in coins.⁵ Coins are easy to obtain, easy to do experiments with, and they are comprised of a wide variety of metallic elements! Aluminum, manganese, iron, nickel, copper, zinc, silver, tin, and gold are all common elements found in coins.^6-8

I decided to do some explorations with coins that involve magnetism. You can see my investigations in the video below:

Video 1: Testing Coins with Magnets, Tommy Technetium YouTube Channel, Published 9/4/19 (accessed 9/5/19)

I’m sure you could have easily guessed that coins which contain mostly iron or nickel, both of which are ferromagnetic, would be strongly attracted to a magnet. But would you have predicted that coins that contain other elements such as silver, copper, or aluminum could also be affected by magnets? I was certainly surprised by this in my investigations! This effect can occur when metals are subjected to the presence of a changing magnetic field. A changing magnetic field can induce electric currents in metals by way of Faraday’s law. These induced electric currents are sometimes called eddy currents. The eddy currents, in turn, generate their own magnetic fields, and the magnetic fields produced by eddy currents can interact with the original magnetic field. It makes sense that stronger eddy currents should be produced in metals that are better conductors, and therefore better conductors should be more responsive to a moving magnet. Because different metals have different electric conductivities (Table 1), it would follow that different metals should interact differently with a moving magnetic field. This is what I observed. Even very large coins made of silver – the most conductive metal of all - could be made to move in the dynamic magnet test! On the other hand, the tiny piece of foil comprised of zinc (which has only one quarter the conductivity of silver) barely budged during the dynamic magnet test.

Table 1: Electric conductivities of some non-ferromagnetic, metallic elements found in coins.

I hope you and your students find some time to examine how strong magnetics affect various coins in the static and dynamic magnet tests described in the video above. If you have some interesting insights or new demonstrations to share, please be sure to leave me a note in the comments. I’d love to learn more about the marvelous interactions between metallic money and magnets.

References:

1. Kuntzleman, T., Attempts to Detect Cocaine on Money: A Great Exploration for National Chemistry Week 2016, ChemEd X, Sept. 2016. (accessed 9/5/19)
2. Kuntzleman, T., Investigations of Hematite Beads: An Experiment for National Chemistry Week, ChemEd X, October 2017. (accessed 9/5/19)
3. Kuntzleman, T., Investigations of Pyrite Nugget Beads: An Experiment for National Chemistry Week, Part 2, ChemEd X, October 2017. (accessed 9/5/19)
4. Kuntzleman, T., The Chemistry of Outer Space, ChemEd X, July 2018. (accessed 9/5/19)
5. Tretiakov, A., Detection of Nickel Cations in Coins, ChemEd X, May 2019. (accessed 9/5/19)   
6. Brunning, A., Periodic graphics: the compositions of U.S. coins, Chemical & Engineering News, July 2016, Volume 94 Issue 28.  (accessed 9/5/19)   
7. Rohrig, B., The Captivating Chemistry of Coins, ChemMatters, April 2007.  (accessed 9/5/19) 
8. Yeoman, R. S. A Guidebook of United States Coins, 72^nd Edition, 2019, Whitman Publishing LLC, Pelham, AL.
9. Engineering ToolBox, (2008). Electrical Conductivity of common Materials.  (accessed 9/5/19)