Expert: Jayendra Upadhye - 2/12/2007

Question
what is refraction? give a simple example that would illustrate the change in velocity as a body goes from one medium to another?

Answer
Hi Niru,
Sorry for the delay!
Imagine you are riding a horsedrawn carriage of two wheels.
you approach a sand bank at a glancing angle.
your left wheel hits the bank first.
The increased friction, slows your left side.
the horses respond to the sudden pull by turning involuntarily left to adjust their load.
in due time, your right wheel hits the sand bank too (a split second later actually).
Now the carriage runs evenly, but at an angle from its original path, and at a slower speed.

After a while, you emerge onto hard ground again.
this time the right wheel will emerge first.
making the horses regain their original direction due to sudden lightening of burden to their right.
a moment later the left wheel is also freed, and the horses continue faster along original direction.

Now replace the horses with photons to left and right of a beam.
repalce the carriage by a "wave front".

And the picture becomes clear!

Light slows down in denser media (sand banks) and travels faster in less dense media..(reaching C in absolute space).
C is 300,000 km/sec in absolute vacuum.
it is less in all other media, and the ratio gives their refractive index!!

Viola!!
Hope that suffices.
Jayen