How does it work?
When light propagates from one medium to another, refraction takes place at the surface and the light beam is bent. The greater the change in the speed of light at the boundary surface, the more strongly the light is refracted. When light travels from the air into a diamond, the refraction is very large. That’s why diamonds sparkle so beautifully.
This demo uses gel balls that are often found at flower shows. The speed of light in the gel balls is very nearly the same as in water, hence the light is hardly bent and the balls appear almost invisible in water.
