Magnetism . One of the aspects of electromagnetism, which is one of the fundamental forces of nature. Magnetic forces are produced by the movement of charged particles, such as electrons, which indicates the close relationship between electricity and magnetism. The framework that unites both forces is called electromagnetic theory. The best known manifestation of magnetism is the attractive or repulsive force that acts between magnetic materials such as iron. However, in all matter more subtle effects of magnetism can be observed. Recently, these effects have provided important clues to understanding the atomic structure of matter.
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- 1 History
- 2 Magnetic field
- 3 Modern theory of magnetism
- 4 Types of magnetic materials
- 5 Applications
- 6 See also
- 7 Sources
- 8 External links
More than two thousand years ago in the city of Magnesia in Turkey a black rock was discovered which attracted iron, which they named magnetite or lodestone, and the force of attraction is known as magnetism, and the object that it exerts a magnetic force is called a magnet.
The regions where the force of the magnet is concentrated are called magnetic poles.
Later the compass was discovered by hanging on a piece of thread and thin from the black magnesia rock it always circled and deviated pointing one end to the north pole and the other to the south pole.
William Gilbert ( 1540 – 1603 ) established the law of magnetic force which says:
“Like magnetic poles repel and magnetic poles attract”
The lodestone or magnetite, an iron oxide that has the property of attracting iron objects, was already known to the Greeks, the Romans and the Chinese. When a lodestone is passed over a piece of iron, it in turn acquires the ability to attract other pieces of iron. The magnets thus produced are ‘polarized’, that is, each of them has two parts or ends called north and south poles. There are no isolated poles, no matter how many times a magnet is broken in half, each resulting piece will be a magnet with a north pole and a south pole. Like poles repel, and opposite poles attract.
The compass came into use in the West as a navigational instrument around 1300 BC. In the 13th century , the French scholar Petrus Peregrinus conducted important research on magnets. His discoveries were not surpassed for nearly 300 years, until the British physicist and physician William Gilbert published his book, De Magnete in 1600. Gilbert applied scientific methods to the study of electricity and magnetism. He observed that the Earth also behaves like a giant magnet, and through a series of experiments he investigated and refuted various misconceptions about magnetism accepted at the time.
Later, in 1750 , the British geologist John Michell invented a balance that he used to study magnetic forces. Michell showed that the attraction or repulsion between two magnetic poles decreases as the square of the distance between them increases. The French physicist Charles de Coulomb, who had measured the forces between electric charges, later verified Michell’s observation with great precision.
A magnetized bar or a current-carrying wire can influence other magnetic materials without physically touching them because magnetic objects produce a ‘magnetic field’. Magnetic fields are often represented by ‘magnetic field lines’ or ‘lines of force’. At any point, the direction of the magnetic field is equal to the direction of the lines of force, and the intensity of the field is inversely proportional to the space between the lines. In the case of a bar magnet, the lines of force exit from one end and bend to reach the other end; These lines can be thought of as closed loops, with one part of the loop inside the magnet and one part outside.
At the ends of the magnet, where the lines of force are closest, the magnetic field is stronger; on the sides of the magnet, where the lines of force are farther apart, the magnetic field is weaker. Depending on their shape and magnetic force, different types of magnets produce different patterns of lines of force. The structure of the lines of force created by a magnet or any object that generates a magnetic field can be visualized using a compass or iron filings. Magnets tend to orient themselves along magnetic field lines. Therefore, a compass, which is a small magnet that can rotate freely, will be oriented in the direction of the lines.
By marking the direction that the compass points by placing it at different points around the source of the magnetic field, the diagram of lines of force can be deduced. Similarly, if iron filings are shaken on a sheet of paper or plastic over an object that creates a magnetic field, the filings are oriented along the lines of force and thus allow their structure to be visualized.
Magnetic fields influence magnetic materials and charged particles in motion. Generally speaking, when a charged particle travels through a magnetic field, it experiences a force that forms right angles with the particle’s velocity and with the direction of the field. Since force is always perpendicular to velocity, the particles move in curved paths. Magnetic fields are used to control the trajectories of charged particles in devices such as particle accelerators or mass spectrographs.
Modern theory of magnetism
Magnetism is the result of the movement of electrons in the atoms of substances. Therefore magnetism is a property of charge in motion and is closely related to the electrical phenomenon. According to classical theory, the individual atoms of a magnetic substance are, in effect, tiny magnets with north and south poles. The magnetic polarity of atoms is based primarily on the spin of electrons and is only partly due to their orbital motions around the nucleus.
Furthermore, the magnetic fields of all particles must be caused by moving charges and such models help us to describe the phenomena. The atoms in a magnetic material are grouped into microscopic magnetic regions to which the denomination of domains applies. All atoms within a domain are thought to be magnetically polarized along a crystal axis. In an unmagnetized material, these domains are oriented in directions to the orange blossom. A dot is used to indicate that an arrow is directed out of the plane, and a cross indicates a direction in the plane. If a large number of domains are oriented in the same direction the material will show strong magnetic properties.
Types of magnetic materials
The magnetic properties of materials are classified according to different criteria.
One of the classifications of magnetic materials – which divides them into diamagnetic , paramagnetic, and ferromagnetic- is based on the reaction of the material to a magnetic field. When a diamagnetic material is placed in a magnetic field, a magnetic moment is induced in it in the opposite direction to the field. It is now known that this property is due to the electrical currents induced in individual atoms and molecules; these currents produce magnetic moments opposite to the applied field. Many materials are diamagnetic; those with the most intense diamagnetism are metallic bismuth and organic molecules which, like benzene, have a cyclic structure that allows electric currents to establish themselves easily.
Paramagnetic behavior occurs when the applied magnetic field aligns all the magnetic moments already existing in the individual atoms or molecules that make up the material. This produces a global magnetic moment that adds to the magnetic field. Paramagnetic materials usually contain transition elements or lanthanides with electrons desapareados.El paramagnetism in nonmetals usually characterized by a temperature dependence: the intensity of the induced magnetic moment varies inversely with temperature. This is because as the temperature increases, it becomes increasingly difficult to align the magnetic moments of individual atoms in the direction of the magnetic field.
Ferromagnetic substances are those that, like iron, maintain a magnetic moment even when the external magnetic field becomes zero. This effect is due to a strong interaction between the magnetic moments of the individual atoms or electrons in the magnetic substance, causing them to line up parallel to each other.
Under normal circumstances, ferromagnetic materials are divided into regions called ‘domains’; in each domain, the atomic magnetic moments are aligned in parallel. The moments of different domains do not necessarily point in the same direction. Although a normal piece of iron may not have a total magnetic moment, its magnetization can be induced by placing it in a magnetic field, which aligns the moments of all domains.
The energy used in the reorientation of the domains from the magnetized state to the demagnetized state is manifested in a lag of the response to the applied magnetic field, known as ‘hysteresis’.
A ferromagnetic material ends up losing its magnetic properties when heated. This loss is complete above a temperature known as the Curie point, named after the French physicist Pierre Curie, who discovered the phenomenon in 1895 . (The Curie point of metallic iron is about 770 ° C).
In the last 100 years, there have been numerous applications of magnetism and magnetic materials. The electromagnet, for example, is the basis of the electric motor and the transformer. In more recent times, the development of new magnetic materials has significantly influenced the revolution of computers or computers.
It is possible to manufacture computer memories using ‘bubble domains’. These domains are small regions of magnetization, parallel or antiparallel to the global magnetization of the material. Depending on whether the meaning is one or the other, the bubble indicates a one or a zero, so it acts as a digit in the binary system used by computers. Magnetic materials are also important components of tapes and disks for storing data.
Large, powerful magnets are crucial in many modern technologies. Maglev trains use powerful magnets to lift themselves above the rails and prevent friction. High-intensity magnetic fields are used in nuclear magnetic resonance imaging, an important diagnostic tool used in medicine. Superconducting magnets are used in the most powerful particle accelerators to keep the accelerated particles on a curved path and focus them.