I was not sure if I should write it here or on Physics board, but I will give a try.
As I understood current (generally emf) can be generated in a system by varying magnetic flux.
For example, let's take AC generator. A loop of wire rotates between N and S magnets.
\$ \Phi = B \times A \times cos(\Omega)\$, where \$ cos(\Omega)\$ is the angle between the magnetic field B and normal of the loop A.
So the maximum flux can be achieved when the normal of the loop is parallel with magnetic field. But why emf at that moment is 0? And why emf is max when flux is 0?