What is a magnetic field?
We explain what a magnetic field is, its origin and the types that exist. In addition, intensity, direction and Earth’s magnetic field.
The magnetic fields are dipolar, have a North Pole and a South Pole.
The mathematical representation of the way in which magnetic forces are distributed in the space surrounding a magnetic source is understood as a magnetic field.
In other words, a magnetic field is a field of forces that is always surrounding a source of magnetic energy, and it is in this region where the elements sensitive to magnetism interact with it, such as ferromagnetic metals. In other words, outside this magnetic field the effects of magnetism do not occur.
Magnetic fields are dipolar, have a North pole and a South pole, which are also called positive pole and negative pole. And for their study, these fields are described in a vectorial way, which means that they are understood as a set of forces endowed with direction and magnitude, which can be represented through vectors in a grid.
Whenever there is a source of magnetic energy, there will be a magnetic field around it, describing how these magnetic forces act.
The mode of interaction between magnetic fields in electrical devices, such as transformers or electromagnets, is a matter of study for the science of magnetic circuits, and has useful implications for the handling of electricity.
Origin of a magnetic field
For a magnetic field to exist, there must also be a source of magnetic energy, such as a magnet or an electromagnet, or an electric current in motion.
There is a correlation between electricity and magnetism as described by Ampère’s Law and Maxwell’s equations, so magnetic fields and electric fields usually correspond. The presence of magnetic fields can be checked using a device known as a magnetometer.
Magnetic field types
An electromagnet is generated by the displacement of the charges of an electric current.
Magnetic fields can be classified according to their source of creation, as follows:
- Magnetic fields from a magnet. They are those that are created naturally by a magnet or by magnetized metal, and that are consequence of the movement of the electrons around the atomic nucleus of this element and also on its own axis, in a rotation known in physics as spin.
- Magnetic fields from current. They are those generated by the displacement of the charges of an electric current, as occurs in electromagnets, in which an electric charge is circulated through a metallic material, thus achieving that it is immediately magnetized and generates a field around it. These fields can also occur around high-voltage electrical devices, such as transformers.
Magnetic field strength
The intensity of the magnetic field is a property that refers to two different forms of magnitude of the magnetic forces acting within it, and that are:
- Magnetic excitation or H field. Understanding magnetism in much the same way as electricity, it describes how intense the energy of the magnetic field is in a specific, point region of it. In other words, it is determined according to the relationship of the field with its electrical sources.
- Magnetic induction or B field. Considered by physicists to be the true measure of magnetic field strength, it is determined by the amount of magnetic flux per unit area in a given region of the field. In other words, it is determined according to the effects that the field produces on its loads.
Direction of a magnetic field
The closer you are to the magnetic source the more it will determine your direction.
The direction of a magnetic field is described using force lines or vectors, which are lines in charge of signaling the direction where magnetic forces converge, or where they push a load that is subject to the magnetic field.
In this sense, the magnetic excitation (H) or magnetic induction (B) variables of the intensity of a magnetic field are vectorial, given that their values change according to the proximity of the region of the field studied, with respect to the magnetic source or pole. In less words: the closer you are to the magnetic source, the more intense the effect will be and the more it will determine its direction.
Earth’s magnetic field
The Earth’s magnetic field deflects the impact of radiation from the sun.
Our planet has a huge natural magnetic field, called a magnetosphere or geomagnetic field. It is a consequence of the constant movement of the ferromagnetic metals that compose it, such as iron and copper, mostly, a consequence at the same time of the terrestrial rotation.
This field plays very important roles in maintaining the world’s electrical balance, diverting the impact of radiation from the sun (the so-called solar wind) as well as rejecting other forms of electromagnetism from space, which could be harmful to life (such as cosmic rays).
The compasses we use for navigation react to this enormous field, always indicating the north, and also the specialised senses of many migratory animals, which thus possess an innate sense of orientation that always takes them to the same region during specific periods of their lives.