The ratio of the speed of light in a vacuum to the speed of light in the material is called as index of refraction. The correct option is A.
The speed of light is the light traveling with the speed inside the vacuum i.e equal to 3 x 10⁸ m/s.
Suppose light is falling on the glass have velocity with angle of incidence and refracted into the glass medium at different velocity and angle of refraction r.
The index of refraction of any medium is the ratio of speed of light in a vacuum to the speed of light in the glass.
Thus, the correct option is A.
Learn more about speed of light in vacuum.
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