THE MENLO ROUNDTABLE
For the full calculations, see the online version of the Roundtable at http://roundtable.menloschool.org.
e purpose of the experiment is to investigate the relationship that
increasing salinity and changing temperature have upon the refractive index of water. In order to determine how varying the temperature and salinity of water aects its index of refraction, I aimed a laser through a water-lled prism and changed its salt content and temperature, examining how the laser beam moved. Specically, the laser was shone through the prism and onto a wall, and then I marked the place where the laser came into contact with the wall. First I altered the salinity of the water, adding a certain amount of salt for each trial, so that I was able to calculate the salinity every time data was collected. en I siphoned out the salt water, replaced it with fresh water, and altered the temperature of the water, recording the new data points. To be more precise, I used cold water, room-temperature water, and hot water for this part of my procedure. Aer I was nished marking the points on the wall, I measured the distances from each point to the origin (which was where the laser’s end was when there was no prism disrupting its path). With this and the length to a specic part of the prism from the origin, I was able to use trigonometry to nd the angle of refraction. Lastly, with my newly found angle of refraction, I used Snell’s Law to calculate the experimental index of refraction for each salinity and temperature.
Before conducting this experiment, my hypothesis was that higher salinity would lead to a higher refractive index, and a colder temperature would cause a higher refractive index. My reasoning for this expectation was based on what we learned in class about density’s relationship to the index of refraction: the higher the density, the higher the index of refraction. A higher-salinity water is denser than a lower-salinity water, and low-temperature water is denser than high- temperature water. With this hypothesis, I dove into my experiment and discovered that the data very closely matched my expectation.