This is the speed of light in vacuum divided by the speed of light in the medium. this determines the amount of bending of a light wave

Refractive index.

Explanation:

Refractive index or the index of refraction may be defined as the quantity that measures how fast the light travels in different media. Different materials have different refractive index.

Refractive index can be calculated by the formula by dividing the speed of light in vacuum with the speed of light in different media. The amount of refraction and the bending of light as light enters from one media to another is shown by the refractive index.

Thus, the answer is refractive index.