Answer
The emf reaches a maximum at $\frac{T}{2}$
Work Step by Step
We can write an expression for the emf $\mathscr{E}$:
$\mathscr{E} = -\frac{d\Phi}{dt}$
$\Phi$ is proportional to the current $i$, so $\frac{d\Phi}{dt}$ is proportional to $\frac{di}{dt}$
In part (c), we found that $\frac{di}{dt}$ reaches a maximum at $t = \frac{T}{2}$
The emf reaches a maximum at $\frac{T}{2}$
