Credit: Sarah Sammis CC-BY-2.0
Q:

# What is the speed of light in water?

A:

The speed of light in water is approximately 225,000 km per second. While enormously fast, this is notably slower than the speed of light in a vacuum, which is 300,000 km per second.

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The degree that light slows down when passing through a medium is described by the index of refraction of that medium. This index measures how much the medium alters the course that the light travels through reflection, refraction, occlusion or other obstruction. Calculating the speed of light in the medium requires dividing the speed of light by the index of refraction. This results in the equation v = c / n, where v is the speed that light travels in the medium, c is the speed of light in a vacuum and n is the index of refraction.

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## Related Questions

• A:

The speed of light when traveling through air is roughly 670,398,880 miles per hour. This number can be determined by dividing the speed of light in a vacuum by the index of refraction of air.

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• A:

When light travels in a vacuum, its speed is 186,282 miles per second. The fastest aircraft, which is the Boeing-43 scramjet, has a speed of 7,546 miles per hour. If these two speeds are compared, the jet's speed is approximately 0.0004 percent that of light.

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• A:

1,802,613,657,600 furlongs per fortnight. This number is easily calculated from the different fixed unit conversions and the speed of light, which is an accepted constant.