Refractive index measurement using total internal reflection

An undergraduate level experiment is presented for demonstrating total internal reflection. The experiment yields a relatively precise value of the refractive index of a prism to be found from a measurement of the incident angle at which total internal reflection occurs. Analytic expressions are obtained for the refractive index as a function of the incident angle for both equilateral and right angle prisms. Students can observe not only the critical angle at which total internal reflection occurs, but measure and analyze the significant rise in reflected beam power. The addition of a small fluid reservoir attached to the side of the prism enables the determination of a liquid refractive index.