This is a simple and effective way to demonstrate induction & Lenz Law. The metal hoops (one open and one closed) are freely moving on a centrally mounted pin. In the product photo above, you have a complete closed circuit (loop) on the right. When a magnetic field is introduced (from a bar magnet being moved toward the closed loop), we have an electrical current and a magnetic field that will repel against the original magnetic field. This is demonstrated when the closed loop moves away from an approaching bar magnet. This is Lenz law. Alternately, when you approach the open circuit (open loop) on the left with a bar magnet, nothing will happen.
The closed loop moves away from the approaching magnet because the current being induced in the closed loop generates a magnetic field that is opposing the bar magnets field. That secondary magnetic field circulating around the loop is repelled by the approaching magnetic field. On the other side, the loop is broken, so the moving magnet cannot induce a current around it.
**Bar Magnet Required (high field strength), not included.