The current i in a coil varies with time as shown in the figure. The variation of induced emf with time would be

In the first T/4  sec current increases at a constant rate and the next T/4 sec it is constant and then it decreases at a constant rate.

$\mathrm{We} \mathrm{know} \mathrm{that} \mathrm{induced} \mathrm{emf} \mathrm{e}=-\mathrm{L}\frac{\mathrm{di}}{\mathrm{dt}}$

$$\begin{gathered} \frac{\mathrm{di}}{\mathrm{dt} } \mathrm{is} \mathrm{constant} \mathrm{so} \mathrm{e} \mathrm{also} \mathrm{will} \mathrm{be} \mathrm{constant} \mathrm{but} \mathrm{in} \mathrm{opposite} \mathrm{direction}. \\ \mathrm{i}.\mathrm{e}. \mathrm{when} \frac{\mathrm{di}}{\mathrm{dt} }\mathrm{is} \mathrm{positive} \mathrm{e} \mathrm{is} \mathrm{negative} \mathrm{and} \mathrm{vice} \mathrm{versa}. \end{gathered}$$