Question

The refractive index of diamond is 2.42. What is the meaning of this statement?

Answer 1

This means that the speed of light in diamond will reduce by a factor of 2.42 as compared to its speed in air. ... In other words, the speed of light in diamond is 1/2.42 times the speed of light in vacuum.

Answer 2

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This statement means that light ray travels 2.42 times faster in air(vaccum) in comparison to diamond.