Total Internal Reflection

[crazy legs]

How come it only happens when light travels from a denser medium to a less dense one, and not the other way around, Thanks.

[jake-the-peg]

This is because of refraction bends the light towards the normal of the boundary as it goes from a less dense medium to a denser one and vice-versa.

So any incident ray will always be bent intowards the denser medium

You can see this on the simulator here:
http://www.ps.missouri.edu/rickspage/refract/r efraction.html

This of course begs the question why it bends towards the normal and not away going into a denser medium.

Look here:

http://hyperphysics.phy-astr.gsu.edu/hbase/geo opt/refr.html

As the light goes slower in the denser medium the bottom part of the wavefront that is already in the denser medium goes slower which has the effect of bending the light towards the normal.


I know that's probably not the best explanation I've ever given - it's kind of hard to put into words - have a look at the diagrams and see if you can see what I mean

[Gef]

Excellent answer jake especially when the question was the "wrong way around".