Fake diamonds in water

Light bends as it passes from one medium (air) to another (glass) because wave velocity and wavelength are medium dependent.

The relationship was first described by Willebrord Snell in 1621 as..

...where the angles have their usual definitions.

The image shows what appear to be huge diamond crystals in water. The photo is a fake but the refractive index difference (1.33 to 2.42) is large and diamonds do still sparkle under water.

If no bending occurs there is no partial reflection and transparent objects are invisible.

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