Hands-on magnet experiments that look closely at particle size

One of my local museums, MiSci, in Schenectady, New York, is a popular hands-on science oriented museum. During my last visit, I was greatly surprised to find a small exhibit with strong magnets that tested the attraction of various iron particle sizes. The exhibit consisted of three vessels filled with liquid (see photo below); at the bottom of each vessel were particles of iron. Each of the three vessels held a different size of iron particles, starting with a "nano" size. Positioned near the vessel were two magnets on vertical sliding rods.

Three vessels with magnets on rods. Each vessel contained different sized
 particles of iron, yet the magnet near each vessel was the same size and strength. 

The purpose of the exhibit was to learn how the particles behave in the presence of the magnet. For the interest of conservation and understanding more about iron particles, this was a wonderful activity to see!

Below is the image of the iron particles that are considered "nano" size or 100 nanometers or 0.1 microns. In the presence of the magnet, the particles are all clustered together very near the magnetic field. As the magnet moves up the vessel the particles stay together following the magnet and traveling easily together in a tight group.

The image below shows a larger size particle, called "magnetite sand" at 1,500,000 nanometers. These particles followed the magnet as it moved up and down on the rod, but did not remain as a tight group. These particles are so small they have fewer magnetic regions that can align to be attracted to the magnet. More about domains can be read in a previous blog post "Magnets are only as strong as ....".

Next is "magnetite powder", at 3,000 nanometers. These particles only slightly are attracted to the magnets. These particles are hardly attached to the magnetic field force. They really just want to sit at the bottom of the container.

So, what is going on here? What might be the difference between "sand" and "powder"? Clearly it is the activity of the small regions, even smaller than the particles called "domains". It is how these domains align in the presence of a magnet that make them attach to a magnet or not.

Learn more about magnets and their many uses in the new publications Magnetic Mounting Systems for Museums and Cultural Institutions. Available for purchase at www.spicerart.com/magnetbook.