Detailed Procedure for Finding the Index of Refraction


•Mag lite (or any lamp/lens combination which produces collimated (straight) light)

•1 m long measuring (2)

(or one 2 m stick)

•Polarizer (1)

•Ring stands (2)



Experimental setup for measuring the Brewster’s angle of a gel sample

Please note that two people are better than one for this experiment.

  1. Make a gel sample according to the procedure above.  Use a mold that allows you to make a brick-like sample a couple of centimeters tall, with a relatively large surface area (such as 10cm by 10cm).
  2. Secure the lamp and the polarizer on the ring stands.  Make sure that the rays from the lamp, the sample, and the polarizer lens all lie along the same line.
  1. With the sample on the ground, point the lamp so that its light touches the sample, and observe the sample from behind the polarizer.
  2. From behind the polarizer, you should observe a significant glare from the lamp as incoming light bounces off the sample into your eyes.

Move your head up and down and find the location at which maximum glare occurs.  This position should be where the angle of incidence equals the angle of reflection.  Keep your head at this position.

  1. Move the polarizer so that the sample is viewed through the polarizer.  Now rotate the polarizer while holding it  until you remove the maximum amount of light possible.  Make a qualitative note of how much glare remains.
  2. Move the sample to a different position along the line of the lamp and the polarizer, and repeat steps 4 and 5.  You may have to move the polarizer vertically as well.  Repeat until finding the sample position that leads to the maximum amount of light removed by the polarizer.