Eddy Current Demonstrator

Quick Answer: Eddy Current Demonstrator reveals Lenz's Law in action, dropping a magnet through a copper tube to show the braking effect of induced eddy currents against an unmagnetized control slug.

The Eddy Current Demonstrator is a straightforward apparatus for demonstrating Lenz's Law in action, using nothing more than a length of tubing and a falling magnet to reveal the braking effect of induced electric currents. It is part of our physics lab equipment India range, built as a physics demonstration kit India classrooms use for core electricity and magnetism concepts.

How It Works

The demonstrator is built around a 12" long copper tube paired with two metal slugs that look identical from the outside but behave very differently when dropped through it. One slug is a plain steel cylinder with rubber end caps; being unmagnetized, it produces no external magnetic field as it falls, so the copper tube has no changing flux to respond to and the slug drops straight through in a fraction of a second, essentially in free fall. The other slug is a strong neodymium magnet, also fitted with rubber end caps to protect both the tube and the magnet on impact. As the neodymium slug moves down the tube, its magnetic field sweeps past each section of the copper wall in turn, and by Faraday's Law of electromagnetic induction, this changing flux induces circulating eddy currents within the copper. Lenz's Law states that an induced current always opposes the change that produced it, so these eddy currents generate their own magnetic field that pushes back against the falling magnet, producing a braking force that grows with speed.

What's Included

Each Eddy Current Demonstrator set includes the copper tube together with both test slugs — the steel slug and the neodymium magnet slug — each fitted with rubber end caps for safe, repeated use. Because the two slugs are matched in size and appear identical from the outside, students can be asked to predict which one will fall faster before the demonstration is run.

Technical Specifications

Related Instruments

To build a fuller picture of electromagnetic induction, pair the Eddy Current Demonstrator with our Primary and Secondary Coils apparatus, which demonstrates induction between two separate windings, or with our Hand Held Generator, which lets students generate current directly through mechanical motion.