There are many methods for measuring the refractive index of liquids.1–7 In this note we present a very simple and accurate method that can be used as a teacher demonstration or as a class experiment. We have not found it described elsewhere.
All one needs is an open rectangular container with thin transparent walls (an aquarium will do), a small light source, an opaque strip 3–4 cm wide, and a sheet of paper.
Affix the strip along the middle of one wall of the container, and the sheet of paper on the wall opposite, as shown in Fig. 1. The light source is placed at a convenient distance near the strip. With the container empty, the edges of the shadow of the strip are marked on the paper sheet opposite. Now fill the container with liquid and mark again the width of the shadow, reduced compared to the...