Objective:
– To demonstrate the Lenz law with metal hoops.
Apparatus:
- Metal hoops with needle stand
- Neodymium magnet on a steel bar
Method:
Instructor demonstrates apparatus only.
Warning! The post has a sharp needle point. Handle with care! Neodymium magnets are strong. Keep them away from ferromagnetic metal. Put it back to the plastic container when finished.
Assemble as shown in the picture above.
This demo shows that when a magnetic field is introduced from a bar magnet moving toward or away from the closed hoop, It will create an induced current and the current will generate a secondary magnetic field will repel against the original magnetic field. The closed hoop will move away when the magnet moves towards it, and will follow the magnet when the magnet move away from it.
For the open hoop, since the closed circuit around the hoop is broken, it will not be able to induce current and create magnetic field to repel against the original magnetic field. Therefore, the hoop does not move when the magnet is either moving towards or away from it.