Four little instruments, one octave of spectrum. Each one starts with a question: make your guess, then run the experiment yourself. The strip below stays lit the whole time, showing which wavelengths each experiment is touching. Four manipulations of the same thing.
The visible octave · 750 nm — 380 nm
Everything here runs on the real physics in miniature: dispersion in glass, interference from a CD's 1.6 µm track spacing, the 42° water-droplet cone, and Rayleigh's 1/λ⁴ scattering. Illustrative in scale, honest in mechanism. Want a full optical bench with lenses, mirrors, and dispersive glass you arrange yourself? The open-source Ray Optics Simulation is the deep end of this pool.