Key Stage 3 (KS3) Waves Practice Test

What is the approximate speed of light in water?

300,000,000 m/s 225,000,000 m/s 150,000,000 m/s 100,000,000 m/s

Correct Answer:

225,000,000 m/s

Explanation:

The speed of light in water is significantly slower than its speed in a vacuum, which is approximately 300,000,000 meters per second. When light travels through a medium like water, its speed decreases due to the interactions with the molecules in the substance. In water, the approximate speed of light is about 75% of its speed in a vacuum, which calculates to around 225,000,000 meters per second. This reduction in speed is a result of the refractive index of water, which is about 1.33. The refractive index indicates how much the light slows down as it enters the material compared to its speed in a vacuum. Thus, the answer of approximately 225,000,000 m/s accurately reflects the behavior of light when it travels through water.

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