Induced emf is called back emf, why?

What is back emf ?

Fill ups The direction of induced e.m.f is such that it always ………………the change which ………….it.

Two identical loops, one of copper and other of aluminium are rotated with the same speed in the same magnetic field. In which case the induced emf and induced current will be more? Why?

Plot a graph showing variation of induced emf with the rate of change of current flowing through a inductor coil.