One of the major difficulties that students find in the basic subjects of Electricity and Magnetism is the understanding of the magnetic properties of matter. In particular, the determination of the directions of magnetic vectors in simple devices constructed with ferromagnetic materials such as magnets, transformers and electromagnets. The confusion is compounded by the misinterpretation of B-H curves and /or M-H curves. Textbooks on basic subjects do not address the issue, although it is possible to make a simple model based on the fundamental laws without resorting to advanced knowledge of electromagnetic theory. First we propose a strategy to understand under what conditions the H vector may have the same or different direction than B in electromagnets with ferromagnetic core, although M and B always have the same direction in these materials. The development leads naturally to the understanding of the influence of the constructive characteristics in obtaining more or less intense magnetic fields in permanent magnets.
Keywords:
ferromagnetism; magnetic vectors; magnets
