ake a graph of Sine of Refraction Angle vs. Sine of Incidence Angle. Draw the best straight line through the points. Measure the slope of the line The ratio of the sine of the incidence angle to the sine of the refraction angle is called the index of refraction (n). In the graph for this experiment, the slope is the ratio of the index of refraction of the incident medium to the index of refraction of the refractive medium. Thus, the slope is ni/nr. The incident medium in this experiment is air. The refractive medium is clear acrylic (or glass). Calculate the index of refraction of the clear acrylic (or glass)