This experiment shows one way to find the index of refraction of Jello. Jello is a common delectable treat enjoyed by many kids. It is also a translucent material which makes it a perfect candidate for an index of refraction experiment. Index of refraction is one of the most important concepts in optics and is an important basis for many interesting phenomenon. Through this experiment, kids can learn and become interested in science while having fun!
Step 1: Make Jello
Create a semicircle shaped piece of Jello using a semicircle petri dish. Follow instructions on jello box. Any color may be used. The semicircle shape will ensure accurate and easily detectable and measurable refraction from laser.
Step 2: Setup
Set up the experiment by first placing the slider rail on top of the books (or a suitable substitute) to elevate the jello. Place the protractor holder in the middle of the slider, and then put the protractor on the protractor holder. Place the semi-circle jello petri dish on the protractor. Place the laser at the end of the rail so it points directly at and over the protractor.
Step 3: Place Jello
Line the Jello up to the 90 degree line so that the laser is perpendicular to the flat jello surface.
Step 4: Collecting Data
Rotate the angle measuring platform 10 degrees more each time (10, 20, 30 etc) and record the angle that the laser exits the jello on the other side. Repeat this until the laser is hitting the jello at 90 degrees (completely parallel). Repeat this step 2 more times for a total of 3 trials.
Step 5: Calculating the Refractive Index of Jello
Snell's Law will be used to determine the index of refraction. Snell's Law gives a relationship between the angle of incidence Θ_1 and its medium's refractive index n_1 and the angle of refraction Θ_2 and its medium's refractive index n_2 using the equation n_1*sin(Θ_1) = n_2 * sin(Θ_2). The medium that the angle of incidence travels through in this case is simply air, whose refractive index is known to be approximately 1, and so we can simplify the previous equation and solve for the refractive index of the jello: n_2 = sin(Θ_1)/sin(Θ_2). Average the refraction angle at each degree measured and create a graph of the sines of refraction angles vs. the sines of incidence angles (The X values are the refracted angles, and the Y values are the incidence angles). Create a line of best fit from the data. The refractive index of Jello will be the slope of this line.
Our graph (shown above) had a best fit line with a slope of 1.21, which told us that our experiment supported that the refractive index of jello is 1.21.
Upon completion of this experiment, we learned many things. We realized that it can be difficult to see the refracted light from a red laser in cherry Jello. This difficulty could have resulted in refraction angle measurement errors, which will lead to an incorrect index of refraction. In future experiments we would advise using a lighter color. However, we believe that this is a beneficial experiment for learning because this method can be used to find the index of refraction of most transparent materials, which will be useful for any optics student.