The flux rule for motional emf can be stated as: d[itex]\phi[/itex]/dt = -[itex]\epsilon[/itex] I have some questions regarding this. 1) Should I find this rule intuitive? And secondly a proof of this rule is given in my book, which I have attached. I don't really understand the idea of the proof - is the idea to proof the above rule or to just proof that if it works, it will do so for loops, which "do not even maintain a fixed shape". Because the words seem to suggest the later but on the other hand that would mean that the above rule is generally unproved in my book.