Explain why the reactance offered by an inductor increases with the increasing frequency of an alternating voltage.
Hint: The reactance of the inductor depends on the rate of change of current.
Step 1: An inductor opposes the flow of current through it by developing a back emf according to Lenz's law. The induced voltage has a polarity so as to maintain the current at its present value. If the current is decreasing, the polarity of the induced emf will be so as to increase the current and vice-versa.
Step 2: Since the induced emf is proportional to the rate of change of current, it will provide greater reactance to the flow of current if the rate of change is faster, i.e., if the frequency is higher. The reactance of an inductor, therefore, is proportional to the frequency. Mathematically, the reactance offered by the inductor is given by
