Ray Optics

Refraction, total internal reflection and a lens bench with real images.

0/2challenges

Angle of incidence°

Upper medium (beam starts here)

Lower medium

Refraction angle: 60.64°
Critical angle: 41.15°
Reflected: 9.6%
Transmitted: 90.4%

The model

Refraction follows Snell's law, n₁ sin θ₁ = n₂ sin θ₂. Going from a dense medium to a thinner one, beyond the critical angle sin θc = n₂ / n₁ no light gets through: total internal reflection, the trick that keeps light inside an optical fibre.

The share of light reflected comes from the Fresnel equations for unpolarised light. The lens bench uses the thin lens equation, 1/f = 1/d₀ + 1/dᵢ, and the three principal rays.

Try this

Put diamond on top and air below, then tilt the beam past 24.4 degrees. That tiny critical angle is why diamonds sparkle. On the bench, move the object inside the focal length and the image flips to the same side, upright and virtual.

Geometric optics: rays, a flat interface, thin lenses and monochromatic light, so no dispersion or diffraction. Educational model, not an engineering design or validation tool.

Achievements0/2

Total internal reflection +30Trap the beam with total internal reflection.
Focus +30Bring an image into focus on the screen.

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