A portable kit for refractive-index studies: refraction and critical angle in solids and liquids

Abstract This paper presents a portable and simple refractive index kit that lets students study refraction, refractive index, and the critical angle in both solids and liquids. In schools, refraction is typically taught using a ray box that produce bright and dim rays, making refraction hard to observe. In addition, the activity also requires drawing lines on paper to trace the rays, which is time consuming and slows the process of teaching and learning. To overcome this problem, the portable refractive index kit uses a monochromatic 532 nm laser beam with a rotating mount and a fixed protractor as the sample stage, making the rays easy to observe without paper tracing and speeding up the lesson. In addition, the kit also offers added value by including a liquid container that enables refractive-index studies of liquids using the same geometry as solids without changing the setup. These additions save time, improve repeatability, and enable clear measurements for both solids and liquids within a single lesson. Refractive index is estimated using Snell’s law from a straight-line Snell plot, and the critical angle for total internal reflection is used as a built-in check. Results for typical classroom samples are n = 1.56 for glass, n = 1.33 for water, and n = 1.45 for cooking oil, with critical angles of 40.17°, 48.75°, and 43.60° respectively. The uncertainties of n , obtained from standard error analysis, range between ± 0.01 and ± 0.02 depending on the measurement method. This project contributed to physics education by providing a low cost, accurate and easy to obtain experimental kit for schools. This innovation adds value to teaching and learning by improving visibility, reducing setup time, and enabling fair comparison between solids and liquids within a single lesson.