Passive Components

Passive electronic components are fundamental parts of electronic circuits that operate without external power and do not generate or amplify energy. Examples include resistors, capacitors, and inductors, which do not provide gain, amplification, or signal directionality in circuits.

A passive element is an electrical component that neither produces power nor energy but instead dissipates, stores, or releases it. Common passive elements are resistors, capacitors, and inductors (also known as coils). In circuit diagrams, these components are typically labeled as Rs (resistors), Cs (capacitors), and Ls (inductors). They usually work alongside active components like semiconductor devices, such as amplifiers or digital logic chips.

Resistors
Resistors are basic components used to limit current flow within a circuit. Each resistor has two interchangeable leads with a material inside that resists electrical current. This resistance is measured in ohms (Ω). By controlling current and causing voltage drops, resistors help manage voltage levels throughout a circuit. According to Ohm’s law,
𝐸
=
𝐼
𝑅
E=IR, where
𝐸
E is voltage,
𝐼
I is current, and
𝑅
R is resistance. Current flowing through a resistor is directly proportional to voltage and inversely proportional to resistance; higher resistance means lower current.

Ohm’s law enables calculation of voltage, current, or resistance when the other two are known.

Capacitors
Capacitors are components that store and release electric charge, consisting of two conductive plates separated by an insulating material called a dielectric. Their ability to store charge is called capacitance, measured in farads (F). Capacitors block direct current (DC) because electrons cannot pass through the dielectric, but they allow alternating current (AC) to flow by continuously charging and discharging. This makes capacitors useful for AC coupling—passing AC signals while blocking DC.

Coils (Inductors)
Coils or inductors are components made of wire wound into loops, sometimes around a magnetic core like iron or steel. When current flows through a coil, it creates a magnetic field that stores energy. Inductance is measured in henries (H). Inductors play an essential role in energy storage and filtering in circuits.

Filter Circuits
Filter circuits use combinations of passive components to block unwanted frequencies and allow desired signals to pass. A common example is an RC-series filter, where a resistor and capacitor are connected in series to control frequency response, such as in high-pass or low-pass filters.