A Low-Cost Smartphone Polarimeter and Malus’s Law

The use of smartphones in the introductory physics laboratory has recently received attention since it provides the possibility to perform a variety of didactic experiments. Smartphones equipped with several built-in sensors, controlled by appropriate software, allow students to explore physical phenomena and carry out various measurements of physical quantities. In this article, after a brief historical introduction about the discovery of light polarization and the development of the polariscope/polarimeter, we describe a low-cost and easily constructed smartphone polarimeter that provides a quantitative way of experimenting with light polarization. In particular, we discuss a didactic activity concerning the use of the smartphone ambient-light sensor to measure the intensity of light coming through two properly oriented polarizing filters, which follows the well-known Malus’s law.