The semicircular lens. From the activity sheet on geometric laser optics, Write down the focal length (UNITS TOO) of the inner and outer rays. a. When you have selected five rays on the laser box and semicircular lens with its straight edge facing left and positioned at the center of the ruler scale. Inner ray __________________ Outer ray _______________________ b. When you turned the lens around so that the curved surface is facing left, with the straight edge on the center of the ruler scale. Inner ray __________ Outer ray __________ 4. (5.4)Refractive index measurement a. What was the refractive index, when you placed the semicircular lens centrally on the template with its straight side facing left?(using Snell's law)