Question

In an $LR$ circuit $f=50Hz,L=2H,E=5$ volts, $R=1\Omega$ then energy stored inductor is

• A. 50 J
• B. 25 J
• C. 100 J
• D. None of these

Answer 1

Answer: (D)

$L=2H,E=5$ volts, $R=1\Omega$
Energy in inductor $=\frac{1}{2}L{I}^2$
$I=\frac{E}{Z}$
$I=\frac{5}{\sqrt{R^2+(\omega L{)}^2}}=\frac{5}{\sqrt{1+4{\pi }^2\times 50^2\times 4}}$
$=\frac{5}{\sqrt{1+(200\pi {)}^2}}=\frac{5}{200\pi }$
Energy $=\frac{1}{2}\times 2\times \frac{5\times 5}{200\times 200{\pi }^2}$
$=6.33\times 10^{-5}$