Fermat’s Principle

This interactive simulator explores Fermat's Principle in Optics & Light. OPL = n₁AP+n₂PB vs hit point; minimum = Snell path. Use the controls to change the scenario; watch the visualization and any graphs or readouts to connect the model with lectures, labs, and homework.

Who it's for: Best once you already know the basic definitions and want to build intuition. Typical context: Optics & Light.

Key terms

  • fermat's
  • principle
  • fermat principle
  • optics
  • light

Live graphs

How it works

Between two fixed points in different homogeneous media separated by a plane interface, the physically realized ray is the one that makes the optical path length n₁ℓ₁ + n₂ℓ₂ stationary (a minimum here). Varying the breakpoint P on the interface traces a smooth OPL curve whose minimum coincides with Snell’s law.

Key equations

OPL = n₁ |AP| + n₂ |PB| → min over P on interface
⇒ n₁ sin θᵢ = n₂ sin θₜ