Critical Angle is an interactive HTML5 Canvas simulation demonstrating the critical angle and total internal reflection for GCSE Physics (Waves topic, 4.6.2). Light travels upward from a glass block (n = 1.50) toward the boundary with air. A single draggable angle slider lets pupils vary the angle of incidence in the glass and watch the outgoing ray respond in real time across three regimes:
- Below 41.8° — the ray refracts out into the air, bending away from the normal, with a faint partial reflection back into the glass.
- At exactly 41.8° (the critical angle) — the refracted ray grazes along the boundary at θ₂ = 90°, flagged with a gold “at the critical angle” banner.
- Above 41.8° — no light escapes; the ray is totally internally reflected back into the glass, shown full-strength with a “total internal reflection” banner.
Four live readouts track the angle of incidence (θ₁), the refracted angle (θ₂, showing “90°” at the critical angle and “none” during TIR), the fixed critical angle (θc = 41.8°), and the current effect. A “Go to critical angle” button (or the C key) snaps straight to 41.8° for instant projector demonstration. It uses the standard ClassAdapt design system: light/high-contrast default theme, dark-navy toggle, and the full Adapt accessibility suite (Irlen overlays, CVD filters, reading ruler, dyslexia spacing, reduce motion, classroom mode, keyboard shortcuts, aria-live announcements), with Lexend and Inconsolata as house fonts.
Search phrases
For library indexing and discoverability:
- critical angle simulation
- total internal reflection
- TIR GCSE physics
- critical angle glass air boundary
- angle of incidence refraction interactive
- Snell’s law critical angle
- light refraction dense to less dense medium
- refracted ray 90 degrees boundary
- GCSE waves critical angle
- total internal reflection demonstration
- optics ray diagram interactive
- refractive index 1.50 glass critical angle
- when does total internal reflection occur
- critical angle calculation arcsin
- SEND adaptive physics simulation refraction