Huygens' Ruler

thingiverse

This is a custom ruler for drawing wave diagrams of light & how it diffracts. It's based on the Huygens' principle, that waves propagate by every point in space radiating spherically: https://en.wikipedia.org/wiki/Huygens_principle So you can use a nail or thumb-tack to secure one end of the ruler, and then draw out the radiating patterns. There's markings to allow you to change the 'phase' of the wave, so you can see effects like beamforming in action. More details here: https://tinkeringsdotorg.wordpress.com/2018/11/30/huygens-ruler-drawing-interference-patterns/