Complete each stage to unlock the next one.
Fibre optic cables carry internet data as pulses of light around the world. Surgeons use thin glass fibres to illuminate the inside of your body. Diamonds sparkle because light bounces inside them dozens of times before escaping. They all exploit the same phenomenon — light that cannot escape a denser material. How can light be trapped?
Fibre optic cables carry internet data as pulses of light around the world. Surgeons use thin glass fibres to illuminate the inside of your body. Diamonds sparkle because light bounces inside them dozens of times before escaping. They all exploit the same phenomenon — light that cannot escape a denser material. How can light be trapped?
When light travels from a denser medium (like glass) to a less dense one (like air), at steep enough angles it cannot pass through — it is completely reflected. This total internal reflection enables fibre optics, endoscopy, and brilliant gemstones.
Total internal reflection occurs when light travels from a denser medium (n₁) to a less dense medium (n₂ < n₁) at an angle greater than the critical angle. At exactly the critical angle, the refracted ray travels along the interface (90°). Beyond it, no refraction occurs — all light is reflected.
For glass (n = 1.5) to air (n = 1): sin θ_c = 1/1.5 = 0.667, so θ_c = 41.8°. Any ray hitting the glass-air interface at more than 41.8° is totally internally reflected. Fibre optic cables exploit this: light enters a thin glass fibre and repeatedly undergoes total internal reflection along its length, even around bends. Signals travel at the speed of light in glass (~200,000 km/s) with very little loss. A single hair-thin fibre can carry thousands of phone calls simultaneously. Medical endoscopes use bundles of optical fibres — some to illuminate the scene, others to carry the image out. Diamonds are cut with steep facets so most light entering from above undergoes total internal reflection multiple times before exiting upward, creating the characteristic sparkle.