Welcome to Spinning Numbers! Learn about electricity and electrical engineering, explained at the level of an undergraduate EE student.

Circuit sandbox

Circuit sandbox is a simulator. Run it in English, o en español.
Help translate Circuit Sandbox into other languages. It’s easy!


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.


The operational amplifier is the building block of analog electronics.


Using a diode in a circuit.


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

Where does the name Spinning Numbers come from?

These videos and articles began as my contribution to Khan Academy where I was the Electrical Engineering Content Fellow in 2016. Since then all the articles have been significantly improved. The addition of simulation models brings the ideas to life. I hope this material helps you in your quest become an electrical engineer.
- Willy McAllister