What is back emf ?

A coil of metallic wire is stationary in non-uniform magnetic field. What is the e.m.f induced in the coil?

What is back bonding ?

n cells, each having emf e, are connected in series what is the emf of the combination?

A cell of e.m.f. 4 V and of negligible internal resistance is connected in series with a potentiometer wire of length 400 cm. The e.m.f. of a Leelanche cell is found to be balacned at 150 cm from the positive end of the potentiometer wire. What is the e.m.f. of the Leclanche cell ?

Induced emf is called back emf, why?

When current in a coil changes with time, how is the back e.m.f. induced in the coil related to it?