physikanten & co // News // Dead Sea Science // Part 3: Saltwater as a light refractor

Part 3: Saltwater as a light refractor

The Dead Sea lies 428 metres below sea level, assuming that is the level of the world’s oceans. Water from Jordan flows into it but cannot flow out, instead it can only evaporate. The salt is left behind, giving the Dead Sea extraordinary properties.

Everyone knows that you can lay in the Dead Sea and read a newspaper. But I find it more interesting what happens, when you twist around in the water in the sea. Many infinite streaks emerge. The water “shimmers” in a similar way to air above a fire.

Why is that?
Light spreads out at different speeds in different materials. The relationship between the speed of light in a vacuum to the (slightly smaller) speed of light in a particular medium is called the Refractive Index. The bigger the refractive index, the stronger the refraction of light at the surface between the two mediums. Diamonds are crystals with a very big refractive index of 2.42, which is why it sparkles much more in comparison to cheap jewellery.
Dirk Schemionek from the Technical University of Dortmund has kindly confirmed the refractive index of my sample from the Dead Sea. His result, measured at 26°C is:
n = 1.395

To give a comparison:
n (air) = 1.0003
n (water) = 1,33
n (window glass) = 1,52

As the less concentrated saltwater with a smaller refractive index is lighter, it collects at the surface of the water. If you were to now mix up the water layers with their various refractive indexes, there would be chaotic refraction and the appearance of many streaks.

Still more extreme is the effect when you pour fresh water into the sea…

---> Click here to go to part four.

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