Re: How do you physically measure the angle of refraction in water using laser?

Here is a simple procedure for determining the index of refraction of a 
liquid.  The liquid can be water, alcohol, or any transparent fluid.

1)	On a white sheet of paper, trace around a transparent, flat-sided 
box.  The box that pushpins come in will work fine.  On this outline, draw 
a normal line to one side and near one edge.  See photo "1." 

2)	Align the laser so that it strikes the side of the box at the 
normal and at an angle to the normal.  Anything between 25 and 45 degrees 
should work just fine.  
3)	You will note that the laser passes relatively straight 
(neglecting the refraction at the sides of the box) through the box.  You 
will see a laser spot on the exit side of the box.  Mark your paper 
directly below this spot.  The angle from the normal to this line is the 
incident angle.  See photo "2."

4)	Slowly fill the box with your liquid.  Enough liquid should be 
place in the box to "submerge" the laser beam. 
5)	At this point you will note that the beam has become refracted and 
is no longer above the incident point marked on the paper.  Mark this new 
location on the paper.  The angle from the normal to this point is the 
refracted angle.  See photo "3."

6)	Remove the liquid and the box.  With the normal line and the two 
reference points, you can now determine the incident and refracted rays.  
The index of refraction of the liquid can easily be calculated from n sin 
(theta) = n' sin (theta').   See photo "4."



A simple and very quick and dirty run-through of this procedure resulted 
in the index of refraction for tap water to be 1.298.  More precise 
measurements and greater experimental care can result in a much more 
accurate value.