Question

In a coil, the current changes form –2 A to +2A in 0.2 s and induces an emf of 0.1 V. The self-inductance of the coil is :

• A. 5 mH
• B. 1 mH
• C. 2.5 mH
• D. 4 mH

Answer 1

Answer: (A)

5 mH

Answer 2

The induced emf in a coil is given by:$(\text{Emf})_{\text{induced}} = -L \frac{di}{dt}$
In terms of magnitude:
$|\text{Emf}_{\text{induced}}| = \left| L \frac{di}{dt} \right|$
Given:
$|\text{Emf}_{\text{induced}}| = 0.1 \, \text{V}$
$\frac{di}{dt} = \frac{2 - (-2)}{0.2} = \frac{4}{0.2} = 20 \, \text{A/s}$
Now, solve for $L$:
$0.1 = L \times 20$
$L = \frac{0.1}{20} = 0.005 \, \text{H} = 5 \, \text{mH}$