An overview of the basic components found in modern electronics - capacitors, diodes, inductors, resistors and transistors

Most modern electronic devices consist of several key components: transistors, capacitors, resistors, inductors and diodes. Often, they are supplemented by additional components like crystals and oscillators, electromechanical components like relays and switches, and connectors.
The key components are categorized into active and passive devices.
Active components rely on an external power source to control or modify electrical signals. They inject power into a circuit and are capable of electrically controlling and amplifying the flow of electrical current, whereas passive components cannot. Passive components don’t need an external power source to function and only require the current traveling through the connected circuit. They either consume or store energy.
A simple way to test whether a component is active or not is to measure the difference be-tween its input and output signals. If there is a decline in power, the component is passive. If the signal is amplified, it is active.
A special type of component is the integrated circuit (IC) where large numbers of transistors, resistors, diodes, and other electronic components are packaged onto a tiny silicon chip (i.e., a microchip).
Passive devices
CapacitorcapacitorThe capacitor is a passive electronic component with two terminals. Its function is to store electrical energy in an electric field and deliver it to the circuit when needed. The capacity of a capacitor to store electrical charge is known as the capacitance of that capacitor. Capacitors play three important roles in an electronic circuit: charging and discharging; maintaining the voltage at the same level; and removing noise.
DiodediodeThe diode is a two-terminal electronic component that allows an electric current to pass in one direction (low resistance) while blocking it in the reverse direction (high resistance). The diode is made up of a semiconductor device with P-type material and N-type material. Common applications include turning alternating current (AC) to direct current (DC), isolating signals from a supply, and mixing signals. The most widely known modern application for diodes is in light-emitting diodes (LEDs). These use a special kind of doping so that when an electron crosses the n-p junction, a photon is emitted, which creates light.
InductorinductorThe inductor – also called as a coil, choke or reactor – is a passive two-terminal electrical component. Its main purpose is to slow down current surges or spikes by temporarily storing energy in an electro-magnetic field and then releasing it back into the circuit.
ResistorresistorThe resistor is a passive electrical component that introduces resistance to the flow of electric current in an electrical circuit to reduce the current. The resistor’s ability to reduce the current is called resistance and is measured in ohms. One of the main uses of resistors is to regulate the current in circuits containing LEDs and transistors. These devices are sensitive to the amount of current and need specific amounts to function properly.
Active devices
TransistortransistorOne of the most important electronic devices, a transistor is a three-terminal semiconductor device used to amplify or switch electronic signals and electrical power. Based on their construction, transistors are categorized into bipolar junction transistors (BJTs) and field effect transistors (FETs). Read our in-depth explainer on transistors.