Lenz's Law

Public summary: 

What happens when we drop a magnet through a pipe? Experiment with dropping them through perspex and metal pipes and see if there's any differences.

What happens when we drop a magnet through a pipe?
Useful information
Kit List: 

Perspex Pipe
Copper Pipe
(We don't have but an aluminium pipe would also be useful)
Some small magnets
Green Iron Filling Paper

Packing Away: 

These currently live in Electromagnetism box, however they may move to floating soon.


Get a volunteer to hold the pipe and challenge them to put the magnet it and catch it as it comes out. If you've got a group ask them if they'd like the copper or perspex pipe, the copper pipe is the much better choice as it means you'll have more time.

This is because the moving magnet is inducing an electrical current in the metal. There are two ways to explain why this causes it to slow down:

[easier]Some energy is needed to make the electrical current (like turning the handle before). This time the energy comes from the falling magnet, and when it loses kinetic energy it slows down.

[harder]Eddy currents of electricity are formed, and these create an electromagnetic effect opposing the motion of the magnet, hence it slows down.

There is also green 'iron filing' paper, which shows up the movement of a magnet through it. You can use this to 'see' the movement of the magnet inside the copper pipe.

People may say it's to do with the metal being magnetic, but it's really not. Copper is not magnetic, try sticking the magnet to the outside of the tube and it won't.

Risk Assessment
Date risk assesment last checked: 
Thu, 30/01/2020
Risk assesment checked by: 
Conor Cafolla
Date risk assesment double checked: 
Thu, 30/01/2020
Risk assesment double-checked by: 
Beatrix Huissoon
Risk Assessment: 
Hazard Risk Affected Person(s) Likelihood Severity Overall Mitigation Likelihood Severity Overall
Powerful magnets Powerful magnets shattering, possibly causing cuts/splinters. All 3 3 9 Warn visitors if you give them a magnet.
Use the minimum number of free magnets. Keep the magnets under control.
Cover with tape to reduce impact, and contain any shards.
Pad edges of magnet to reduce finger trap.
Call first aider in case of injury
1 2 2
pipes Any pipe hitting people in face. All 4 2 8 Demonstrator should hold pipe for younger kids and monitor use for others.
Call first aider in case of injury.
2 1 2