Question

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

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

We know that,

$E_{ind}=-L\frac{di}{dt}$

$\text{During 0 to}\frac{T}{4}:$

$\frac{di}{dt}=\text{constant}\Rightarrow E_{ind}=-\text{constant}$

$\text{During}\frac{T}{4}to\frac{T}{2}:$

$\frac{di}{dt}=\text{0}\Rightarrow E_{ind}=0$

$\text{During}\frac{T}{2}to\frac{3T}{4}:$

$\frac{di}{dt}=\text{constant}\Rightarrow E_{ind}=+\text{constant}$

$\text{During}\frac{3T}{4}toT:$

$\frac{di}{dt}=\text{0}\Rightarrow E_{ind}=\text{0}$

On plotting the induced emf against $t$, we have


Hence, $\left(A\right)$ is the correct answer.