I want to build a simple induction apparatus like the one displayed at this web page: http://micro.magnet.fsu.edu/electromag/java/faraday/" [Broken] My first attempt didn't work, and I'm trying to troubleshoot it. I am wondering how much magnetic field degradation there is around the toroid. As the switch is closed and a magnetic field is created, how strong is the magnetic field by the time it gets to the other solenoid on the other side of the toroid? It could be that nearly all of the field strength is preserved around the toroid, or it could be that it is much weaker on the other side. Does anyone have any idea how much the field degrades around the toroid? Perhaps this apparatus works in principle, but is not very efficient in practice. Thanks.