Engineering Principles V11

Clive W. Humphris

INDUCTORS: Inductive Reactance.  

The opposition to current change in an inductor is called reactance and given the symbol XL (AC resistance) and expressed in Ohms. The back-EMF generated opposes the applied current change.

Whilst capacitors inhibit the flow of direct current and allow the passage of alternating currents, inductors exploit the opposite effect, they resist AC and allow DC to pass through. Therefore, inductors have a low reactance (AC resistance) at low frequencies which increases as the frequency is increased. Compare the graph waveforms for capacitive and inductive reactance, the Xc gives an exponential waveform and XL is a straight line.

You will see the effect of combining capacitive and inductive reactance when we look at tuned circuits.

Inductive reactance is proportional to the applied voltage frequency. Applying AC Ohm's Law using XL in place of R and will prove that as the frequency is increased so the current decreases.

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