The Floating Compass: A Demonstration of Electromagnetism and Lenz’s Law

An electromagnet is formed when the magnetic field is produced by an electric current, usually running through a wire coil. The floating compass is an easy, visual explanation of this and Lenz’s Law, formulated by Heinrich Lenz in 1833. Lenz’s Law states that the direction of the current will always flow such that it is opposite of the change in magnetic flux, or the measurement of the total magnetic field passing through a given area. Lenz’s Law is also oftentimes incorporated with Faraday’s Law which allows the same coordinate system to be used for both the flux and the electromotive force (EMF). For this reason, it could also be used as an introduction to Faraday’s law. The Floating Compass contains a needle that has been magnetized, then poked through a straw so it floats in a tank of water. A coil of wire is partially submerged in the water so that the middle of the circle of the coil is where the water ends. This coil is then attached to a switch and D4 batteries set up in parallel, creating a circuit with a current running through the coil, forming an electromagnet. Since the needle has been magnetized, it will then either go through the loop or be repelled. By flipping the switch the other way, the current’s direction is flipped and the direction of the poles change, causing the needle to either do the opposite, demonstrating Lenz’s law. Having the magnetized needle floating on water stems from a discovery that Francois Arago made in 1822. He noticed that when the horizontal needle of a compass was suspended away from all foreign bodies, it settled at true north much faster than it did when it was not. This being true means that a needle floating in water, which is both away from foreign bodies which would affect oscillations necessary to settle and lacks surface friction and resistance, would come to rest much faster. For this reason, the needle in this experiment is floating (in water). This project is very easy to replicate-all that is needed is a needle, a bar magnet, a straw, a container filled with water, some wire, D4 batteries, alligator clips, and battery holder packs (which are affordable/often readily available). The demonstration is also easily comprehensible, makes it a great project for teachers to use in the classroom to teach the concept of electromagnetism, Lenz’s Law, and maybe even the basics of Faraday’s law. These are all important branches of physics, and this is an easy way to explain them to people of all ages. The floating compass itself does not have many modern-day applications, though it can be fun to play with as well as demonstrating a concept that is very widely used. Electromagnetism is used in many electrical appliances to produce magnetic fields, including speakers, motors, generators, hard disks, MRI machines, and many more. Electromagnetism was discovered over 200 years ago and every year, people find new genius ways to utilize it.