Welcome to Spinning Numbers! Learn about the world of electricity and electrical engineering. The concepts are taught at the level of an undergraduate EE major just starting out. These videos and articles began at Khan Academy where I was the Electrical Engineering Content Fellow in 2016.

Circuit sandbox

The shiny new feature of Spinning Numbers is a simulator, the Circuit sandbox.

Circuit sandbox screenshot

Check out Circuit sandbox in English or Circuit sandbox en Español.


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Become familiar with the most important electrical quantities: charge, current and voltage. Get a first look at engineering numbers, units, and notation. Read a summary of the math and science preparation that will help you have the best experience studying electrical engineering.

Circuit elements

Circuits are made of components: resistors, capacitors, and inductors, and sources: voltage and current. Ideal and real-world elements. We develop a precise vocabulary for talking about circuits.

Circuits with resistors

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

What’s with the name?

Where does the name Spinning Numbers come from?


Interesting questions and answers about electrical topics that need a home.

Coming soon

DC circuit analysis

Learn Kirchhoff’s Laws and the methods of circuit analysis: node voltage, mesh current, and loop current methods.

Natural and forced response

Circuits with capacitors and inductors change with time. The natural and forced response of RC, RL, and RLC circuits. This is where we start to use calculus.

AC circuit analysis

If we limit ourselves to signals shaped like sines, a whole method of AC analysis emerges. We’ll be able to figure out what happens in circuits with any signal. AC methods are far simpler than solving a differential equation from scratch.


Circuit sandbox is a simulator for modeling circuits.