|MadSci Network: Physics|
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.
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