Basic Refraction question. Kindly help

[helpphysics]

Homework Statement

A fisherman in a stream 20 cm deep looks downward into the water of stream
and sees a rock on the stream bed.
How deep does the stream appear to the fisherman?

Homework Equations

We Assume that the index of refraction of the water is 1.33.

The Attempt at a Solution

I am not able to apply the normal angle equation here..nuts !

 

[helpphysics]

Kindly let me know the formula concept and i will calculate myself. I am really not getting it.
Thanks in advance

 

[Stonebridge]

The formula is derived according to the following theory.
It's a method for measuring refractive index using apparent depth, but you can apply it to your problem quite easily.

 

[helpphysics]

Thanks mate. You really explained me the concept behind it too
Thanks once again. yoyo !