the switch S1 is closed at time t = 0 and the switch S2, is keot open. At some later time (t0), the switch S1 is opened and S2 is closed. The behaviour of the current I as a function of time 't' is given by:
Self Inductance -
An emf is induced in the coil or the circuit which oppose the change that causes it. Which is also known back emf.