Total Internal Reflection

Total internal reflection is a phenomenon where light arrives at the boundary between two media and is completely reflected (no refraction). This occurs when the index of refraction of the first medium is larger than the index of refraction of the second medium: 

n₁ > n₂

and only occurs if the angle of incidence is greater than the critical angle. In our demo, we use a spiral-shaped piece of acrylic. Inside the spiral (when illuminated from one of the ends), light will reflect many times before emerging on the other end, but the shape of the spiral ensures that each angle of incidence will be larger than the critical angle.

Total internal reflection is how fiber optics cables work, allowing for long-distance, high-speed data transfer.