A choke coil has a self-inductance of 20 mH . If the magnetic...

The magnetic potential energy $U$ stored in an inductor of self-inductance $L$ carrying a steady current $I$ is given by the formula:

$U = \dfrac{1}{2} L I^2$

Given:
$L = 20\text{ mH} = 20 \times 10^{-3}\text{ H}$
$U = 90\text{ mJ} = 90 \times 10^{-3}\text{ J}$

Substituting the given values into the formula:

$90 \times 10^{-3} = \dfrac{1}{2} \times 20 \times 10^{-3} \times I^2$

$90 = 10 \times I^2$

$I^2 = 9$

$I = 3\text{ A}$

Answer: $3\text{ A}$