Optics Puzzle: Lenses & Mirrors
An original ray-tracing puzzle built for this syllabus — drag and rotate plane mirrors, concave and convex mirrors, and convex and concave lenses to guide a real light beam into the goal across six levels. Every reflection and refraction is computed live from true geometry: mirrors reflect using the exact local surface normal at the point the beam strikes (correctly reproducing the true focal length f = R/2 and even genuine spherical aberration for off-axis rays), and lenses bend the beam using the same paraxial transform that produces all three of the textbook's principal-ray rules from one general formula, so any ray — not just the special ones drawn by hand — refracts correctly. All six levels solved by an independent search before release to confirm each is actually completable.
Law of reflection: angle of incidence = angle of reflection
Drag the body of the mirror or lens to reposition it. Drag the small ring beside it to rotate.
The gold beam is real ray-tracing — every reflection and refraction is computed from the actual geometry, live, as you move things. It turns teal when the beam reaches the goal.
Mirrors reflect using the true local surface at the exact point the beam strikes it — angle of incidence equals angle of reflection, every time, on flat or curved glass alike.
Lenses bend the beam according to its height above the optical axis and the lens's focal length — the same rule produces every principal ray your textbook draws by hand, and every ray in between them too.
Element Key
Plane mirror — flat, simple reflection
Concave mirror — converges, real focus
Convex mirror — diverges, virtual focus
Lens — bulges out (convex) or in (concave)