Passive Components in AC Circuits

Introduction

Electrical and electronic circuits consist of many different components that are connected together to form a complete and closed circuit. Among these components, the resistor, capacitor, and inductor are the three primary passive components used in electrical circuits.

Electric current can flow through a circuit in two different ways. If the current flows in one steady direction only, it is classified as Direct Current (DC). However, when current continuously changes its direction and magnitude, it is known as Alternating Current (AC).

Passive components in AC circuits behave very differently compared to their behavior in DC circuits because they introduce impedance rather than just resistance. Passive components consume electrical energy but cannot amplify or increase the power of an electrical signal. Since they do not generate energy, their power gain is always less than one.

In AC circuit analysis:

R represents resistance
C represents capacitance
L represents inductance

Resistors in AC Circuits

Resistors behave the same way in both AC and DC circuits. The resistance value of a resistor remains constant regardless of the supply frequency. In a purely resistive AC circuit, the voltage and current are always in phase. Therefore, the instantaneous power consumed can be calculated by multiplying the instantaneous voltage and current values.

Capacitors and Inductors in AC Circuits

Unlike resistors, capacitors and inductors oppose the flow of alternating current through a property known as reactance. The reactance of an inductor is called inductive reactance (X_L), while the reactance of a capacitor is known as capacitive reactance (X_C).

Although reactance also restricts current flow, it differs from resistance because it is not constant. The reactance of an inductor or capacitor depends on:

The frequency of the AC supply
The physical value of the component (inductance or capacitance)

As a result, the opposition offered by capacitors and inductors changes with frequency, making AC circuit behavior more complex than DC circuits.

Conclusion

Passive components play a vital role in AC circuits. While resistors offer constant resistance, capacitors and inductors introduce frequency-dependent reactance. Understanding how these components behave in AC circuits is essential for analyzing and designing efficient electrical and electronic systems.