Electromagnetic Induction in Physics

Induction is what happens when a magnetic field refuses to stay still. Change the flux through a loop and a voltage appears across it, whether the change came from moving the loop, moving a magnet, or simply letting the field itself swell and fade. Nothing about the loop's own charge is involved, so the rule cannot be stated in terms of forces on moving electrons alone. The minus sign carries real physics as well, since Lenz's law says the induced current always arranges itself to fight the very change that created it. The blocks run from the definition of flux through the law itself, then through the two ways of producing the effect, motion and changing fields, and finish with the generator, which turns this opposition into the mains supply.