Refraction of light

[romesh]

I have a question regarding refraction.

 

I want to know the reason for the decrease in the speed of light in mediums like air, water, kerosene etc...

 

If you could help me I would also like to know the reason as to why some mediums are opticaly rarer and some opticaly denser.

 

 

[StringJunky]

The apparent slowdown is caused by the additive time effects of absorption and emission of a photon through consecutive molecules in its path. In a transparent medium the absorbed photon transfers insufficient energy to an electron to enable it to overcome the energy threshold that would allow to go the next higher energy level or orbital...if it did the material would be classed as opaque.