In this paper we show how to obtain the inverse-square law of the distance for the light intensity emitted from a small source in a simple, fast and with good precision way. With the aid of two smartphones, free apps and a ruler, one is able to measure the distances between these devices (one of them as a source and the other as a measuring light intensity) and the respective light intensities measured by the probeware in the device. The facility of reproduction of the proposed experiment and the penetration of the use of tablets and smartphones among students and teachers, could make the proposed activity a good alternative to the introduction of physical phenomena which exhibit the same functional dependence, such as the universal gravitation law of Newton and Coulomb's Law.
experimental physics teaching; smartphone; inverse-square law
