I decided to simulate this scene in Lord of the Rings for a project in school with the purpose of calculating the "real" mass of the One Ring. I've done the experiments according to this principle sketch but I have some troubles with calculating the magnetic force that the copper coil is exercising on my 3,8 g iron ring. The area of the ring is 5,84 cm2 and I measured the strength of the magnetic field to be 33 mT in the position of the ring. How would you calculate the force FB? I'm really having a problem with this calculation and would very much appreciate an answer. Any simplifications and assumption are very welcome if that is needed. Please do also ask me for more information if that is needed.