To conduct the experiment, I brought about six boxes of orange jell-o, one red laser pointer, one protractor (+/- .5º), a set of different color pencils, 4 medium bowl to make the jell-o in, 4 spoons to stir each of the solution, a measuring cup(accuracy: +/- .125 cups), about 5 cups of hot and cold water, about 15 clear rectangular containers (6cm x 8.5cm x 1cm) used to mold the jell-o, and about 15 sheets of the pre labeled polar coordinate paper. (Attached in appendix)
After I gathered all the materials, I started to make the jell-o. To make the jell-o, I mixed a box of jell-o powder and one cup of hot water (140ºF) together in a medium bowl. Then I stirred the solution with a spoon until as much of the powder is dissolved as possible, approximately two minutes. Next, I added one cup of cold water (70ºF) and stirred for about another minute. Then I got the rectangular molds and poured the solution into them. Finally, I stored them in the refrigerator so the jell-o can cool. I repeated the procedure four times to make the jell-o for all four levels of independent variable.
After the jell-o has been cooled, I took all the jell-o out and set it out at room temperature for about two hours to make sure the temperature is constant for all my trials when I start to measure the refraction. On the polar coordinate paper, I lined up the
Where the laser is at right now is at the location of one of the angle of incidence.
The data collected are recorded in a table along with its graph in the appendix. The following is one of the data collected for the lab and the graph it produced.
Ai in the data represents the incidence angles; the angle that laser light entered the jell-o normal to the surface of the liquid. The angle that the laser light comes out of is the refractive angle.
To calculate the index of refraction, I entered the data into the Logger Pro program and find the slope of the line. The equation states Ni*Sin (Ai) = Nr*Sin (Ar) I rearranged the equation to graph the data where the index of refraction is the slope. After rearranging, the equation becomes:
Y=mx+b
Sin (Ar) = Ni/Nr * Sin(Ai)
“Y”= “m” * “x”
The x axis becomes Sin (Ai) and the y axis becomes the Sin (Ar). The slope is Ni/Nr. I assume that the Ni or the index of refraction of the air is one. The index of refraction of the jell-o is Nr which we can determine by finding the slope of the graph. Ni/slope of the graph will give the index of refraction of jell-o. For the sample trial, the slope is .7527. The index of refraction is 1/.7527= 1.33.
The data in both charts are fairly precise. The values were within no more than .17 of each other.
According to the data given, the index of refraction increase for both 200% water and the 50% water when compared to the control’s value. The 25% of water variable did not work because when the laser went inside the jell-o, the light scattered and come through on a great range of angles on the other side. The uncertainty would have been at least 30º.
The picture to the left is a picture of the refraction of one of the 25% water trials. I can see that the range of the refractive angle is large, so I could not get an accurate result of index of refraction.
The higher the index of refraction meant that the laser light traveled slower as it went through the jell-o. The jell-o with just 25% water had too many particles inside it, so when the light from the laser goes inside the jell-o, the light reflected off of each individual molecules many times and scattered as it went through the jell-o. The light did not come out at a single angle, but at a wide range of angles. Therefore, it was hard to calculate the index of refraction for this variable.
The data I got was not what exactly as I had predicted. I predicted that the 200% water jell-o would have the lowest index of refraction since there were going to be more room for the light to go through the jell-o without having to reflect off of many other gelatin molecules. However, it had a slightly higher index of refraction than the control’s value. Then my prediction for the 50% water was correct though because it did come out to have a higher index of refraction than the control’s index of refraction. The control’s value was 1.14 while the 50% water’s value was 1.43.
Chemically, after the loose protein strains tried to form the new network with water molecules, it makes sense that there will be many protein strands mixed together in very little space which would slow down the path of light since light has to scatter and move through the particles to get to the other side.
There are a few sources of error in the lab. One of the major errors include that the laser light scattered like it did with the 25% water variable, it makes it hard to calculate the index of refraction. A slightly off error on the polar graph can cause a significant error because the units on the graph are so small. Being off by one or two millimeter can mean a two or three degree difference in the refractive angle which could change the slope of the line produced on the graphs. This error could increase or decrease the value of the index of refraction. To correct this error, it is possible to limit the amount of error by repeating the trials more times to reduce all the answers that do not make sense. Continue to repeat the trials until getting consistent results.
Another error could be that the sides of the container are not exactly perpendicular to the line. Rounded edges can cause reflecting of the laser’s beam to different directions. Difference in direction could mean a difference in the refracted angle. It may not be a huge difference, but it can be changed to improve the accuracy of the results. It can simply be corrected using containers that would produce straighter sides.
A third source of error could be the levels of independent variable may be too large or too small to measure and get results that can be compared to see the difference in the refractive index. The amounts I choose were 25%, 50%, 100% (control) and 200% for the volume of water. To correct this problem, it’s possible just to choose levels of independent variable that are more close together. For instance, maybe choose 120% of water and 140% of water instead of a huge gap like 100% to 200%.
