Linear Quadrupole Magnetic Field Measured with a Smartphone

We believe that a natural focus of the physics education research community is on understanding and improving students' learning in our physics courses. Due to the increase in technology, we can bring laboratory experiments closer to our students. It is necessary to update our laboratories technologically to get closer to the world in which our students live. With this in mind, we have considered the magnetic field created by a linear quadrupole and we have studied its dependence on distance, n being the exponent of distance. The main objective of this exercise is for our students to discover that the exponent n is very close to -4. The purpose of this work is to show that a laboratory is a powerful tool that increases significant learning under three conditions: 1) the practice must not be too sophisticated; 2) students must handle objects in the lab; and 3) the practice must be scientifically accurate, including the fitting using the least-squares approximation, and the following and necessary error calculation. We provide this practice so that all interested physics teachers can use it and adapt it to their specific laboratory.