The current i in a coil varies with time as shown in the figure....

Induced emf, $\text{e} = - \text{L} \dfrac{\text{di}}{\text{dt}}$

For $0 \le \text{t} \le \dfrac{\text{T}}{4}$,

i-t graph is a straight line with positive constant slope.

$∴ \dfrac{\text{di}}{\text{dt}} = \text{constant}$

$⇒ \text{e} = - \text{ve}$ and constant For $0 \le \text{t} \le \dfrac{\text{T}}{4}$

For $\dfrac{\text{T}}{4} \le \text{t} \le \dfrac{\text{T}}{2} ,$

$∵$ i is constant $∴ \dfrac{\text{di}}{\text{dt}} = 0$

$⇒ \text{e} = 0$ For $\dfrac{\text{T}}{4} \le \text{t} \le \dfrac{\text{T}}{2}$

For   $\dfrac{\text{T}}{2} \le \text{t} \le \dfrac{3 \text{T}}{4}$,

i-t graph is a straight line with negative constant slope.

$∴ \dfrac{\text{di}}{\text{dt}} = \text{constant}$

$⇒ \text{e} = + \text{ve}$ and constant For $\dfrac{\text{T}}{2} \le \text{t} \le \dfrac{3 \text{T}}{4}$

For $\dfrac{3 \text{T}}{4} \le \text{t} \le \text{T}$,

i is zero $∴ \dfrac{\text{di}}{\text{dt}} = 0$

$⇒ \text{e} = 0$ For $\dfrac{3 \text{T}}{4} \le \text{t} \le \text{T}$

From this analysis, the variation of induced emf with time as shown in the figure below.