Question

When the current changes from +2A to - 2A in 0.05 s, an emf of 9V is induced in a coil. The coefficient of self- induction of the coil is -

• A. 0.2 H
• B. 0.4 H
• C. 0.8 H
• D. 0.1 H

Answer 1

The correct option is D 0.1 H

We know,

$\begin{array}{c}\varphi =li\\ \Rightarrow \frac{d\varphi }{dl}=\frac{Ldi}{dl}\end{array}$

Putting the value.

$\begin{array}{c}\Rightarrow 9=L\left(\frac{4\times 100}{0.05}\right)\\ \Rightarrow L=\frac{9\times 5}{4\times 100}=\frac{9}{4\times 20}\\ \Rightarrow L=\frac{9}{80}\approx 0.1H\end{array}$

Hence,

Option $D$ is correct answer.