Fundamentals of Electrical Engineering

Published by McGraw-Hill Education
ISBN 10: 0073380377
ISBN 13: 978-0-07338-037-7

Chapter 5 - Transient Analysis - Part 1 Circuits - Homework Problems - Page 232: 5.21



Work Step by Step

If steady-state conditions existed, $i_{L}$ would be equal to the steady-state current through $R_{2}$, i.e. no induced e.m.f (electromotive force) in the opposite direction. Current through $R_{2} = \frac{V_{S}}{R_{2}}=\frac{12}{6*10^{-3}}=2mA$ Since $i_{L}<2mA$, there is a small current flowing in the opposite direction to that from $V_{S}$. By Lenz's Law, this current was generated by an e.m.f. in the same direction, i.e. an induced e.m.f which opposed the direction of $V_{S}$ (Faraday's Law). This suggests that the inductor is active and hence that steady-state conditions did not exist just before the switch was opened.
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