Abstract: A wedge-shaped optical component in the form of cordwood system is designed, which is constructed by an isosceles trapezoid glass prism and a glass plate. With this apparatus, we easily test the liquid refractive index according to the principle of equal thickness interference by using a conventional reading microscope and a parallel monochromatic light source. The results show that this apparatus has clear physical meaning, good repeatability, highly precise. It is easy to be operated thus well suited to be popularized in optical laboratories of universities.

Key words: liquid refractive index, isosceles trapezoid glass prism, principle of equal thickness interference test