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Overview of Basic Electronic Components

  • Starter
  • Article
  • Ages 10+
  • 4 min read
A four-band resistor, cylindrical capacitor, amber LED and three-lead transistor photographed up close.

Basic electronic components include resistors, capacitors, diodes, LEDs and transistors. A resistor limits current, a capacitor stores energy, a diode mainly conducts forward, and a transistor switches or amplifies a signal. These are common building blocks in many IoT circuits.

Contents
Four common kinds of parts joined on one line.
  • Resistor
  • Capacitor
  • Diode
  • Transistor

What you will learn

  • Say the main job of each component.
  • Tell a resistor from a capacitor.
  • Describe how these components affect a circuit.

Before you start

It helps to know what voltage is.

What do resistors and capacitors do?

Resistors are commonly used to limit current, divide voltages and pull up I/O lines. What makes capacitors special is their ability to store energy. A decoupling capacitor's job is to suppress high-frequency noise in power supply signals.

The resistor regulates current, the capacitor keeps energy.
  • Current-limiting resistor
  • Capacitor storing energy
  • Energy held back

How do diodes and LEDs pass current?

In normal operation, a diode conducts mainly in the forward direction and restricts reverse current. A sufficiently large reverse voltage can cause breakdown. LEDs also have a forward direction and need suitable current limiting in a practical circuit; forward voltage alone does not limit current.

A diode mainly conducts forward; an LED needs appropriately limited forward current to emit light.
  • Diode
  • Direction of current
  • LED

What can a transistor do?

Driven in cutoff or saturation mode, a bipolar junction transistor (BJT) creates the binary on/off effect of a switch. Transistors can also amplify electrical signals: the output has a similar shape but much higher power, supplied by the power source.

A transistor switches current or makes a signal stronger.
  • Transistor
  • On/off switching
  • Amplified signal

Real-world example

With an adult, look at a photograph of a small circuit board and try to find resistors, capacitors, diodes or transistors. Use the photograph only; this activity does not require touching or powering a board.

Common misunderstandings

A resistor and a capacitor do the same job. A resistor limits current, while a capacitor stores energy.

All diodes block reverse current in the same way. Real diodes have small reverse leakage; if reverse voltage exceeds a threshold, breakdown can occur. Some types, such as Zener diodes, are designed to operate in breakdown.

Frequently asked questions

What is a resistor used for?

To limit current, divide voltages and pull up I/O lines.

What is special about a capacitor?

Its ability to store energy.

What does an LED need to light up?

An LED needs a suitable forward voltage and current limiting in a practical circuit to light up.

What is a transistor for?

As an on/off switch or to amplify electrical signals using energy from a power source.

Summary

  • A resistor limits current and a capacitor stores energy.
  • Diodes and LEDs mainly conduct in the forward direction under normal operating conditions.
  • A transistor switches current or amplifies a signal.

Terms in this article

English and Vietnamese terms, with the meanings used here. Hover, tap or Tab to a term with a dotted underline for an explanation as you read.

VoltageĐiện áp
The difference in electrical potential energy per unit charge between two points.
ResistorĐiện trở
A component used to limit current, divide voltage or pull up I/O lines.
CapacitorTụ điện
A component able to store energy.
Decoupling capacitorTụ tách
A capacitor that suppresses high-frequency noise in power supply signals.
Diode
A component that usually conducts forward; reverse behavior depends on diode type and operating conditions.
Light-emitting diodeLED
A light-emitting diode with a forward voltage required for it to light up.
Transistor
A component used as an electronic switch or to amplify signals.

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Sources

These sources are written for older readers. If they feel hard, read them with an adult.