rephrase the following text: In this experiment, I will be determining the refractive index of a glass block with a ray of light going through the figure using the data provided in the lab. The second purpose of this experiment is to determine the focal length by taking a convex lens, a light source, and a screen and measuring the distance between the image and the lens. The theory in this experiment for a thin lens is 1/f = 1/d0 + 1/di