magnetic field



We explain what a magnetic field is, how it is produced and what its characteristics are. We also tell you about the Earth's magnetic field.

Magnetic fields are dipole, they have a North pole and a South pole.

What is a magnetic field?

A magnetic field is the mathematical representation of the way in which magnetic forces are distributed in the space that surrounds a magnetic source. This source can be a magnet, a load on movement or one electric current (many loads in motion). Whenever any of these elements exist, there will be a magnetic field around it, that is, a field of magnetic forces. Outside of this field there are no magnetic effects.

A fundamental characteristic of magnetic fields is that they are dipole: they have a North pole and a South pole, which are also called a positive pole and a negative pole. Unlike the electric fields that can be generated by electrical charges (such as a electron), there are no “magnetic charges” that generate magnetic fields. Magnetic fields always have two poles associated with them. As a consequence, the magnetic field lines are always closed, as in the case of the magnet: they leave the north pole and arrive at the south pole.

Origin of a magnetic field

For a magnetic field to exist, there must be a source of magnetic energy (such as a magnet), a moving charge, or an electric current.These elements are the only ones capable of creating a magnetic field and the only ones that can be affected by it.

An electric charge (like an electron moving in space) generates a magnetic field around it that will exert a force on another moving charge. The same happens with electrical currents.

The case of magnets is particular because there are no moving charges involved, but rather these materials generate a magnetic field due to certain microscopic phenomena of a certain complexity.

As described by Ampère's Law and Maxwell's equations, magnetic fields and electric fields often exist together in the nature. Certain changes in the time of a magnetic field produce electric fields. A good example of the coexistence of these two fields is electromagnetic radiation, such as light.

The presence of magnetic fields can be checked using a device known as a magnetometer.

Types of magnetic field

An electromagnet is generated by the displacement of charges from an electric current.

Magnetic fields can be classified according to their source of creation:

  • Magnetic fields coming from a magnet. Magnets are materials that have the particularity of having a permanent magnetic field, created by what in physical is known as the spin electrons (can be understood by thinking of it as a spin on themselves). On the other hand, there is metals that can "become" magnets when magnetized by an external magnetic field.
  • Magnetic fields from current. Every charge in motion produces a magnetic field. Therefore, an electric current also produces a magnetic field. For example: electromagnets (like the one in the figure above) are devices in which by means of a battery current is circulated through a wire wound on metal. This current generates a magnetic field around it that magnetizes the metal and generating another magnetic field. Thus, electromagnets are used to generate variable magnetic fields since by changing the current, the magnetic field changes.

Direction of a magnetic field

The magnetic field lines tell us its direction.

Theaddress of a magnetic field can be described using lines or vector, in charge of pointing out the direction towards which the magnetic forces point. In the figure above you can clearly see the lines of the magnetic field generated by the magnet, which indicate the direction of the force with which the magnet interacts with the metal particles.

The fact that the magnetic field has a direction implies that it is a vector. Any force is a vector quantity, that is, it represents a quantity that has a direction and a sense, such as speed. Since the magnetic field is proportional to the magnetic force, then it is also a vector quantity. In fact, it is interesting to note that the magnetic force felt by a moving particle immersed in a magnetic field is always perpendicular to the direction of that field and its own speed.

Earth's magnetic field

The Earth's magnetic field deflects radiation from the Sun.

Our planet has a natural magnetic field, also called a geomagnetic field. In the center of Earth there is cast iron (for the high temperatures). Due to the earth's rotation, this metallic liquid is in constant motion, forming an electric current (as the metal moves, the electrons that compose it move). This current is what produces the Earth's magnetic field that is so intense that it escapes from the Earth's surface.

The Earth's magnetic field plays a very important role since it diverts very dangerous radiation for living beings from the Sun. Without the Earth's magnetic field, the atmosphere it would be destroyed by cosmic rays. The compasses we use for navigation interact with this field: its magnetized needle is always aligned with the Earth's magnetic field, indicating north. Furthermore, many migratory animals use the planet's magnetic field to always orient themselves and move in the same directions during specific periods of the year.

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