Eddy Current Demonstration Apparatus

Quick Answer: The Eddy Current Demonstration Apparatus is a pair of upright metal tubes on a wooden base, with cushioned catch cups at the bottom. A strong magnet dropped down a tube falls slowly because it induces circulating currents in the tube wall, while a non-magnetic piece of similar size falls straight through, showing eddy currents and Lenz’s law.

A Magnet That Falls in Slow Motion

In the listing image, two tall metal tubes stand upright on a wooden base, held apart near the top by a clear acrylic cross bar with a dark support rod in the middle. Each tube ends above a red cup lined with a soft pad that catches whatever is dropped, and two small cylindrical pieces sit on the base. In sets of this kind those pieces are a strong magnet and a non-magnetic slug of similar size, so the class can compare their falls through the same tube.

As the magnet drops, the magnetic flux through each ring of tube wall ahead of it rises and the flux behind it falls. Those changes induce loops of current running round the tube, called eddy currents. By Lenz’s law the currents oppose the change that causes them: the wall ahead pushes back on the magnet and the wall behind pulls on it. The magnet soon reaches a low steady speed at which magnetic drag balances its weight, and the energy it would have gained as motion is turned into a little heat in the tube.

The effect needs a good electrical conductor, not a magnetic one; copper and aluminium are not attracted to a still magnet, yet they brake a moving one strongly. The same principle stops drop-tower rides and some trains without contact. The tube metals, magnet type and whether either tube is slotted along its length should be confirmed at enquiry. A rotating version of the same effect is the Eddy Current Disc Demonstration Model.

Care & Handling

• Strong magnets can snap onto steel objects and pinch skin; keep the magnet apart from tools and the other slug.
• Keep magnets away from phones, bank cards and watches.
• Drop pieces only from the top opening and let them land in the cushioned cup rather than catching them by hand.
• Keep the tube bores clean and dry so that friction does not affect timings.

Specifications

Applications

• Comparing the fall of a magnet and a non-magnetic slug through a metal tube
• Demonstrating Lenz’s law and the conversion of energy to heat
• Timing falls to show that the magnet reaches a steady terminal speed
• Introducing magnetic braking and damping in engineering topics

Why Choose LabEquip

Teachers covering electromagnetic induction in senior secondary physics, and lecturers running first-year college demonstrations, pick this apparatus because the slow fall surprises students and prompts real discussion. LabEquip supplies it through the STEM kits range, and our contact page can answer questions about tube materials.

Frequently Asked Questions

Why does the magnet fall so slowly through the tube?

Its moving field induces circulating currents in the tube wall. By Lenz’s law those currents set up fields that oppose the magnet’s motion, pushing back from below and pulling from above, so it falls at a low steady speed.

Why does the non-magnetic slug fall normally?

It has no magnetic field of its own, so it causes no changing flux in the tube wall and no currents are induced. It falls under gravity with only slight friction, which proves the slowing of the magnet is a magnetic effect.

Is the tube itself magnetic?

No. The effect relies on the tube conducting electricity well, not on it being magnetic. Copper and aluminium are not attracted to a magnet at rest, yet they brake a moving magnet strongly because induced currents flow easily in them.

Where does the magnet’s energy go?

The gravitational potential energy lost during the fall becomes electrical energy in the eddy currents and then heat in the tube wall, instead of becoming kinetic energy as it would in free fall.

What happens if a tube has a slot along its length?

The slot breaks the circular paths that the eddy currents need, so much weaker currents flow and the magnet falls noticeably faster. Comparing a slotted and a complete tube is a common extension to the basic demonstration.

How can students measure the effect?

Time the fall of each piece with a stopwatch, repeat several times and average the results. Dividing the tube length by the time gives the average speed, and a stronger magnet or thicker tube wall gives a longer fall time.

Last Updated: September 2026