Self-Inductance & Energy question from NEET 2011 (AIPMT, Prelims)

Answer: (a)

1. $e = -L\,\dfrac{di}{dt}$, so emf is constant where $i$ is a straight line.
2. $0$ to $T/4$: $i$ rises, $di/dt > 0$, so $e$ is a constant negative value.
3. $T/4$ to $T/2$ and $3T/4$ to $T$: $i$ constant, so $e = 0$.
4. $T/2$ to $3T/4$: $i$ falls at the same rate, so $e$ is an equal constant positive value.
5. So the answer is (a) (negative pulse, then positive pulse).