A passive component is an electronic component that stores energy in the form of current or voltage. They are incapable of providing any net energy gain into a circuit. Passives are unable to make use of the power or energy in a circuit and cannot control current flow. Inductors, Resistors, Capacitors, and Transformers are all examples of passive components.

Also known as a coil or choke, an inductor is a passive electronic component that stores energy within a magnetic field. The magnetic field is created when electricity flows into a wound coil that is wound around a core. An inductor is measured by its inductance. The unit of inductance is the Henry (H).

A resistor is a passive component that regulates the flow of electrical current in a circuit. They are used to reduce current flow in electronic circuits. A resistor is measured by its resistance. The unit of resistance is the ohm (Ω).

A capacitor is a passive component that stores electrical energy in an electric field. They are used in an electrical to store electrical energy, similar to a battery. A capacitor is measured by its capacitance. The unit of measure for a capacitor is the farad (F).

A transformer is a passive component that transfers energy between two or more circuits. They are able to convert one current or voltage to another current or voltage.

An EMI (Electromagnetic Interference) Filter is a passive device used to suppress selected frequencies/interference that show up in a signal or power line. They are made up of capacitors and inductors. Capacitors will force away noise current away from the load. Inductors will reduce/block the signals noise.

SMT (Surface Mount Technology) is the method of creating circuits in which SMD (Surface Mount Device) components can be mounted directly onto the surface of a PCB (printed circuit board). The pads of the SMD component are soldered to the PCB board. These are typically used in automated PCB assembly.

A through-hole component is one which has leads (metal connectors) that come out from the component. Through-hole components are mounted to PCB boards by placing the component’s leads through holes in the board and then soldering them to board manually. Typically used in manual PCB assembly.

An axial leaded component is one that has leads running from each side of the component.

A radial leaded component is one that has leads running from a single side of the component.

Tolerance is the allowable limits of variation for a component’s measured value.