Welcome to Spinning Numbers. Learn about electricity and electrical engineering.

September 16, 2019 — New
Logic gates — summary of gate symbols and how to draw an OR symbol.

May 20, 2019 — The definition of the Ampere has changed.

### Circuit sandbox simulator

Circuit simulator in English, en español, 用简体中文 (Chinese), 日本語で (Japanese).
Can you help translate Circuit Sandbox into other languages? It’s easy!

### Introduction

Become familiar with the most important electrical quantities: charge, current, and voltage.

### Circuit elements

Circuits are made of resistors, capacitors, inductors, and power sources.

### Resistor circuits

Resistors in series and parallel, the voltage divider, delta-wye resistor networks.

### DC circuit analysis

Kirchhoff’s Laws, node voltage method, mesh and loop current methods.

### Special topics in DC analysis

Linearity and superposition. Source transformation. Thévenin and Norton equivalents.

### Natural and forced response

Natural response is what a circuit does with its own internal stored energy.

### AC circuit analysis

If we limit signals to only sine waves, we get AC analysis based on complex exponentials.

### Special topics in AC analysis

Decibels and RMS.

### Amplifiers

The operational amplifier is the building block of analog electronics.

### Semiconductors

Using a diode in a circuit.

### Electrostatics

Electric force is described by Coulomb’s Law. Electric field. Formal definition of voltage.

### Digital electronics

Basic concepts underlying digital hardware design.

A collection of amusing, interesting, (and possibly useful), engineering questions.

### What’s with the name?

Where does the name Spinning Numbers come from?

### Printing

Tips on the best way to print articles from Spinning Numbers.

### Everything

List of everything on Spinning Numbers. Topics, articles, videos, images, and on and on.

### External resources

Glossary of electrical terms

These videos and articles began at Khan Academy where I had the honor of being the Electrical Engineering Content Fellow in 2016. The concepts are explained at the level of an undergraduate EE student. Motivated middle school and high school students can get a lot from the course.

Spinning Numbers web site came to life in 2016 after I completed my fellowship at KA. All the articles have been reviewed and significantly improved, and several new articles have made their appearance. A nice new feature is the Circuit Sandbox simulator. Many articles include simulation models to let you try your test your understanding and bring the concepts to life.