Magnetism? Definition, information and explanation ...
magnetism In addition to gravitation, weak nuclear power, and strong nuclear power is one of the four basic physical forces and based on electromagnetic interactions. Magnetic fields are invisible, but their field lines can be made visible, for example, with iron filings.
On magnet can attract but also repel other magnetic objects. In this context, the poles of the magnet are important. Each magnet has a north and south pole. The same applies here: the same poles repel each other (North Pole - North Pole, South Pole - South Pole), while different poles attract (North Pole - South Pole).
In addition to the so-called permanent magnets, which generate a static and just permanent magnetic field, has the physicist William Sturgeon in the early 19th century the electromagnet developed. Electric current flows through a coil with an iron core, creating a magnetic field. This is retained as long as the current flows through the coil. If you turn off the power, the magnetic field disappears again. Without this invention, u.a. Electron microscopes, electric generators and magnetic resonance tomographs unthinkable.
The earth itself is surrounded by a huge magnetic field, the Earth's magnetic field, surround. In the interior of the Earth, the liquid and iron-containing part of the outer core of the Earth is most likely responsible for the magnetic field. The magnetic poles correspond approximately to the geological poles. However, the Earth's magnetic field is by no means stable. On average, there is a polarity reversal every 250,000 - 300,000 years, which means that the north and south poles change. By the way, one works compass only due to the earth's magnetic field. The compass needle itself is a small magnet and aligns with the poles.
Last but not least, the Earth's magnetic field also has significance for some species of animals. Birds, turtles and numerous fish such as salmon or carp use the magnetic field for orientation. One speaks also of the magnetic sense.
Types of magnetism in solids: