(a) What is self induction? (6)

(b) A coil of 800 turns is wound on a wooden former and a current of 5A is passed through it to produce a magnetic flux of 200 micro-webers. Calculate the average value of e.m.f. induced in the coil when the current is (i) switched off in 0.08 seconds (ii) reversed in 0.2 seconds.