Gradient Refraction Through A Solution

A solution who's refractive index varies with depth.

refraction, reflection Updated on: 06/13/13

To demonstrate refraction of light in the particular case of a solution where the refractive index varies with depth.

Lucite container, sugar cubes and milk powder, laser

Particular care is necessary in the preparation of the sugar solution to obtain best effects in the demonstration. The long lucite container should be half filled with water and allowed to stand overnight. Bubbles which have settled during the night should be brushed out. In order to give very small amounts of scattering add to the water the smallest amount (about 1 cubic millimetre) of powdered milk. When settled add 6 or 7 cubes of sugar evenly spaced along the bottom of the lucite tank. From this point on do not jiggle or disturb the tank while the cubes of sugar are allowed to completely dissolve which takes at least six hours. The solution is then ready for use and provided it is not disturbed it will be satisfactory for demonstrations for another 2 days before diffusion destroys the concentration gradient. If the laser beam is now directed along the length of the solution, the initial direction being slightly down towards the floor of the tank, the light path takes the form of one or two curved loops before emerging (on to a screen if desired) at the far end of the tank. Trial will give a variety of paths but the laser beam should enter at about mid-depth (ie at 2 cm from the base if a solution of depth 4 cm is being used.