Question

As I explained in lecture, the explanation given in your book for the transmission of light through a transparent object and why its speed is slower than in vacuum when traveling through a transparent object is incorrect. What is the correct explanation?

Answer 1

HI there!

The refractive index is basically the main factor passing through a material which slows down light..   n=1 means the light moves at full speed.   Water has an index of refraction around n=1.34.   Thus, this means light moves at 25% slower speed in water than in a vacuum.

Vacuum here is considered to have a refractive index of 1

and air on the other hand has a refractive index of air is about 1.00029

This explains why light travels a little faster in vacuum compared to plain air.

This should be a better and short explaination for the concept

Hope this helps, please hit like :)