What happens to the speed of light when it travels from water to air?

If light travels enters into a substance with a lower refractive index (such as from water into air) it speeds up. The light bends away from the normal line. A higher refractive index shows that light will slow down and change direction more as it enters the substance.

Explanation: I used the internet.

that tool is called an altimeter which measures your altitude which can be used to tell which atmosphere you are currently in, including the stratosphere.

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wavelength divides in half and speed stays the same.