Eddy Current Disc Demonstration Model

Quick Answer: The Eddy Current Disc Demonstration Model shows how induced currents slow a moving conductor without touching it. The listing image shows an aluminium disc on a low-friction bearing mounted on a base, with a copper-coil electromagnet beside its rim; the spinning disc slows sharply when it turns through the magnetic field.

Braking a Disc Without Touching It

Give the eddy current disc a spin with the magnet switched off and it turns freely on its low-friction bearing for a long time. Energise the electromagnet and the disc slows almost at once. Nothing touches it; the braking comes entirely from currents induced inside the aluminium.

As each part of the disc moves into the magnetic field, the flux through it changes, and small loops of current, called eddy currents, swirl through the metal. By Lenz’s law these currents set up magnetic fields that oppose the motion producing them, so they drag on the disc. The disc’s kinetic energy is turned into heat in the aluminium, and the faster it spins, the stronger the drag becomes.

The same effect brakes trains and fairground rides, damps the pointers of some analogue meters and heats pans on induction hobs. The listing image labels the magnet as a copper coil, so its supply requirements, along with the disc diameter, should be confirmed when ordering.

Specifications

Applications

• Demonstrating eddy currents and magnetic braking
• Illustrating Lenz’s law with a rotating conductor
• Discussing induction hobs, metal detectors and train brakes
• Comparing run-down times with and without the field applied

Care & Handling

• Spin the disc by hand at moderate speed only, keeping fingers clear of the rim.
• Keep the gap between disc and magnet free of filings, clips and other metal debris.
• Switch the coil off after each demonstration so it does not overheat.
• Check that the disc runs true; a bent disc can rub against the magnet.

Why Choose LabEquip

Teachers buy this model for the electromagnetic induction topic because it makes an invisible current produce a very visible effect. LabEquip supplies it in the STEM kits range; the Lenz’s Principle Verification Apparatus shows the same opposition with a single ring and a hand-held magnet. Enquire through our contact page.

Frequently Asked Questions

Why does the disc slow down without being touched?

Movement through the magnetic field induces eddy currents in the aluminium. By Lenz’s law these currents produce magnetic fields that oppose the motion, creating a drag force. The disc slows even though nothing is in contact with it.

Where does the disc’s kinetic energy go?

It is converted into heat in the disc by the eddy currents flowing through the metal’s resistance. With a small demonstration disc the temperature rise is slight, but in train brakes the same heating is large and must be managed.

Would a disc with slots cut in it slow down as quickly?

No. Radial slots break up the paths the eddy currents follow, so much smaller currents flow and the braking is weaker. Transformer cores are made of thin insulated layers for the same reason, to cut down wasteful eddy currents.

Why is the disc made of aluminium and not steel?

Aluminium is a good conductor and is not attracted by a magnet, so any braking must come from induced currents. A steel disc would also be pulled towards the magnet, mixing ordinary magnetic attraction with the eddy current effect.

Does the braking force depend on the speed of the disc?

Yes. Faster motion changes the flux more quickly, induces larger currents and gives a stronger drag. As the disc slows, the braking weakens, so eddy current brakes are effective at high speed and are usually combined with friction brakes for the final stop.

Where are eddy currents used in everyday technology?

Magnetic brakes on trains and fairground rides, induction hobs, metal detectors, the sorting of aluminium cans from other waste, and damping in some analogue meters all rely on eddy currents induced in a conductor.

Last Updated: September 2026