Question

In which of these situations would light slow down?

A. from plastic to air
B. from ice to water
C. from a vacuum to air
D. from glass to air

Answer 1

As far as we know, the speed of light is faster in a vacuum than in any other medium. Therefor C is correct. The speed of light would slow down going from a vacuum to air.

Answer 2

Option (C) from a vacuum to air

Step-by-step explanation:

Speed of light in any media depends on the refractive index(n) of the medium in which light is travelling.The medium having least refractive index have the fastest speed of the light.As the refractive index of the vacuum is less(1.0000) than that of the air(1.0003), so the speed of light will slows down while moving from vacuum to air.The refractive index 'n' is the ratio between speed of light in vacuum(c) to the speed at which the light is travelling i.e v, (n = c / v).