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

Circuit sandbox

Spinning Numbers has a circuit simulator, the Circuit sandbox.
Run the Circuit sandbox in English or en Español.


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

Circuit elements

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

Circuits with resistors

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

DC circuit analysis

Figure out the currents and voltges in a DC circuit using Kirchhoff’s Laws, node voltage method, mesh and loop current methods. Linearity and superposition.

Natural and forced response

Natural response is what a circuit does with its own internal stored energy.
Forced response is what happens when you apply an external signal.
Learn a trick for quickly sketching exponential waveforms.

AC circuit analysis

We limit signals to be only sine waves, and develop an analysis method based on complex exponentials. This ends up being much simpler than solving differential equations from scratch every time.


The operational amplifier is the building block of analog electronics.


Here’s a list of everything on Spinning Numbers. Topic areas, articles, videos, images, etc.

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. I hope you enjoy them.
- Willy McAllister