Question

A coil has an inductance of 5H and resistance $20\Omega$ . An emf of $100$v is applied to it. What is the energy stored in the magnetic field, when the current has reached its final value .

Answer 1

given $L=5$H

$R=20\Omega$

$E_v=100$v

When current reaches its final value $L=0$

$I_0=\frac{E_0}{R}$

$=\frac{\sqrt{2}{E}_v}{R}$

$=\frac{100\sqrt{2}}{20}$

$=5\sqrt{2}$A

Energy stored in magnetic field$=\frac{1}{2}L{I}_{\circ }^2$

$=\frac{1}{2}\times 5\times {\left(5\sqrt{2}\right)}^2$

$=\frac{1}{2}\times 5\times 25\times 2$

$=125$J