Question

The index of refraction for water is 1.33 and for glass it is 1.52. What happens to the speed of light when light travels from water into glass?

Answer 1

The speed of light changes according to the index of refraction of the medium:

Explanation:

In vacuum the speed of light is `c=3xx10^8m/s` while in water will be:
`v_("water")=c/n_("water")=(3xx10^8)/1.33=2.25xx10^8m/s`. This new speed is smaller than the one in vacuum.
We expect that in glass will be even smaller:
`v_("glass")=c/n_("glass")=(3xx10^8)/1.52=1.97xx10^8m/s`
We can see a progressive reduction of speed as light passes into media with higher index of refraction.

Answer 2

The speed of light decreases.

Explanation:

The speed of light in a medium is inversely proportional to the refractive index of the medium.

`v=frac{v_0}{n}`, where

`v` is the speed of light in a particular medium.
`v_0=3`x`10^8`m/s is the speed of light in vacuum, whose refractive index is 1.
`n` is the refractive index of the medium.

In water, the speed of light is `frac{v_0}{1.33}=2.26`x`10^8`m/s.

In glass, the speed of light is `frac{v_0}{1.52}=1.97`x`10^8`m/s.