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Julia Heimark

7.2 Error

In order to calculate the percent dierence due to error, I had to do some online research. For the salinity trials, I based my theoretical refractive indexes on a graph at www.reeeeping.com. [3] For the temperature trials, I was only able to nd the theoretical refractive index of one temperature, which I found at www.thermo.com. [2] Using these two sources I was able to calculate my percent dierence for each trial, and the average of them all was 0.25%.

Many likely sources of error could be eliminated or reduced by improvements in the experimental design. One source of error that I encountered was the fact that the set up was not extremely stable. Any extraneous weight or pressure applied to the table that the laser and prism were on would thereby tilt the table slightly and change where the laser entered and exited the prism. Another source of error was that the laser had to be held down for it to remain steady on the table. Although this was almost impossible to avoid, there were other experimental errors that occurred. I observed that the prism’s walls bowed due to water weight. is changed the shape of the prism slightly and aected where the laser hit the wall. is distortion of the prism wall was exacerbated by the hot water test as the walls bowed signicantly more in the hot water test and subsequent tests than in the earlier trials. e fact that I used the hot water before the cold could have caused the deviation of the cold-water observation from my hypothesis. Aer I nished collecting my data, I played around with the prism walls a bit. I noticed that as the walls bowed they caused a noticeably large height dierence, but I did not see it aecting the x-axis displacement. Hence in my measurements I measured the x-axis displacement only and ignored the y-axis displacement to eliminate as much of this error as possible. Lastly, another source of error was the siphoning of the water. When I siphoned out the water, I was unable to remove all the salt that remained from the salty water. e small amount of remaining salt aected the density of the water, which in turn aected the index of refraction.

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