Question:
An inductor coil stores $64 \mathrm{~J}$ of magnetic field energy and dissipates energy at the rate of $640 \mathrm{~W}$ when a current of $8 \mathrm{~A}$ is passed through it. If this coil is joined across an ideal battery, find the time constant of the circuit in seconds:
Correct Option: , 4
Solution:
$\mathrm{U}=\frac{1}{2} \mathrm{Li}^{2}=64 \Rightarrow \mathrm{L}=2$
$i^{2} R=640$
$\mathrm{R}=\frac{640}{(8)^{2}}=10$
$\tau=\frac{L}{R}=\frac{1}{5}=0.2$
Option (4)
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