Fermat's Principle of Least Time

Fermat’s principle states that light travels between two points along the path that requires the least time. This simulation visualizes the principle using a bench with mirrors, a glass rod, a lens, and media of adjustable refractive index, allowing students to see how refraction and reflection affect the travel time of light.

Students can drag the light source and the eye to new positions, use step buttons to progress through the experiment, and adjust sliders that change the refractive index of the lower medium or the glass rod. The race button restarts the light’s journey, while pause and dash controls let users examine the ant‑trail paths that trace the light’s route.

By interacting with the model, learners discover how Snell’s law emerges from Fermat’s principle, how lenses focus light, and why mirrors reflect according to the angle of incidence. The activity reinforces concepts of refraction, reflection, and the relationship between optical path length and travel time, suitable for high‑school physics curricula.