Smartphone use in a physics project on magnetic field measurements

This paper presents a detailed teaching and experimental project on magnetism designed for high school students. The project aims to help students to measure magnetic fields using the "Phyphox" smartphone application and explore how magnetic field strength depends on various physical quantities such as distance, electric current, number of coil turns, and especially the size of the electromagnet core. As a practical example, the project proposes using a permanent magnet and a homemade or laboratory coil, with a variable core made from bundles of iron nails. The paper explains the theoretical background, experimental setup, data analysis and offers guidelines for constructing relevant magnetic field dependencies. Special attention is given to the usability and educational advantages of the "Phyphox" application for high school students. The paper concludes with pedagogical evaluations and recommendations.