Learn About AC Theory!

...after you learn about DC circuits, you need to tackle AC Theory

Damped Tuned Circuit

Welcome. This section of the learnabout-electronics site is here to help you learn about AC Theory. The aim is to explain about AC components and circuits electronics simply, step by step, with the minimum of mathematics and using real components as our examples. You'll find help with calculations and information on how AC components work. There are quizzes too, to test your knowledge as you progress.

Learn More

How does a radio select one station from all the stations on a band? How does a power supply change AC to DC? What is phase change? AC Theory is an essential in many branches of electrical and electronic engineering; audio, video, cell phones, motors, lighting and many other systems use AC components and circuits that act differently to DC circuits. Knowing basic theory is essential to understanding how such complex circuits work.

Vocational Electronics

The theory in this part of "learnabout-electronics" is designed as a linked set of individual learning modules. They can be used as a complete course, or separately to fit the way you want to learn. They provide a solid background theory to "hands on" electronics, and because they cover common topics found in many "Official" electronics syllabuses, they also provide useful information and exercises for students at several levels of experience, with many links to electronics industry sites in the learnabout-electronics links section for further information.

Step by Step

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You can select any module or single section within a module to study, but as each module leads on from the previous one, the best way to learn is Step by Step Starting with Module 1. See what you will learn as each module starts by telling you (in they grey box) just what you need to know, then study each section (numbered 1.1, 1.2 etc) in turn, and use the revision questions at the end of the module to help check your understanding, before going on to the next module. Easy!

Know what you will learn

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Each module is divided into several smaller sections or pages. Every module and section has a "What You Will Learn" panel that tells you just what you should learn from that module or section.

Check your learning

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Revise as you learn with the revision questions in each section, and the "Module Quiz" at the end of the module.

Prefer Paper?

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If you would like a paper version of any module to print and keep, click the PDF icon at the top of the page in each module, to download a printable copy of the complete module.

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Step by Step Features

red bulletEach of our learning modules has been designed using tried and tested educational methods, to take you from a basic knowledge of DC electronics, step by step through the essentials of "Alternating Current" theory.


red bulletAnimated diagrams help explain important concepts.


red bullet Each module has a built in assessment so you can check your own progress towards a thorough understanding of theory.


red bullet Theory is learned without complex circuit analysis, concentrating on understanding practical electronics.


red bullet Essential maths topics are explained "Step by Step" and you can download a free booklet on how to solve Electronics Maths problems. (There is even a free scientific calculator to download and use on your PC!)


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