Answer:
the speed of light in glass is 1.52 times smaller than in a vacuum
Step-by-step explanation:
The speed of light in a medium is given by:
where
c is the speed of light in a vacuum
n is the refractive index of the medium, which is a number always greater than 1.0
From the formula, we see therefore that when light enters a medium, its speed decreases.
In particular, for glass the index of refraction is
n = 1.52
Therefore, this means that the speed of light in glass is 1.52 times smaller than in a vacuum.