The ancient Greeks, originally those near the city of Magnesia, and also the early Chinese knew about strange and rare stones (possibly chunks of iron ore struck bylightning) with the power to attract iron. A steel needle stroked with such a 'lodestone' became 'magnetic' aswell, and around 1000 the Chinese found that such a needle, when freelysuspended, pointed north-south.
The magnetic compass soon spread to Europe. Columbus used it when he crossedthe Atlantic ocean, noting not only that the needle deviated slightly from exactnorth (as indicated by the stars) but also that the deviation changed during thevoyage. Around 1600 William Gilbert, physician to Queen Elizabeth I of England,proposed an explanation: the Earth itself was a giant magnet, with its magneticpoles some distance away from its geographic ones (i.e. near the points defining the axis aroundwhich the Earth turns).
Magnetismus
The Magnetosphere
On Earth one needs a sensitive needle to detect magnetic forces, and out inspace they are usually much, much weaker. But beyond the dense atmosphere, such forces have a much bigger role, and aregion exists around the Earth where they dominate the environment, a regionknown as the Earth's magnetosphere. That region contains a mix of electricallycharged particles, and electric and magnetic phenomena rather than gravity determine itsstructure. We call it the Earth's magnetosphere
Magnetism is a force generated in matter by the motion of electrons within its atoms. Magnetism and electricity represent different aspects of the force of electromagnetism, which is one part of the universe ’ s fundamental electroweak force. The region in space that is penetrated by the imaginary lines of magnetic force describes a magnetic.
- Magnetic Field Units. The standard SI unit for magnetic field is the Tesla, which can be seen from the magnetic part of the Lorentz force law F magnetic = qvB to be composed of (Newton x second)/(Coulomb x meter).
- Terms in this set (29) True or False: the strength of an electromagnet can be increased by reducing the number of turns on the wire coil.
- This video provides an introduction to basic concepts in magnetism, including magnetic poles, magnetic fields, and electromagnets. It is a useful reference f.
- Magnetism is an invisible force or field caused by the unique properties of certain materials. In most objects, electrons spin in different, random directions. This causes them to cancel each other out over time. However, magnets are different. In magnets the molecules are uniquely arranged so that their electrons spin in the same direction.
Only a few of the phenomena observed on the ground come from themagnetosphere: fluctuations of the magnetic field known as magnetic storms andsubstorms, and the polar aurora or 'northern lights,' appearing in the nightskies of places like Alaska and Norway. Satellites in space, however, sensemuch more: radiation belts, magnetic structures, fast streaming particles andprocesses which energize them. All these are described in the sections thatfollow.
But what is magnetism?
Until 1821, only one kind of magnetism was known, the one produced by ironmagnets. Then a Danish scientist, Hans Christian Oersted, while demonstratingto friends the flow of an electric current in a wire, noticed that the currentcaused a nearby compass needle to move. The new phenomenon was studied inFrance by Andre-Marie Ampere, who concluded that the nature of magnetism wasquite different from what everyone had believed. It was basically a forcebetween electric currents: two parallel currents in the same direction attract, in oposite directions repel. Iron magnets are a very special case, which Ampere was also able to explain.
What Oersted saw...
In nature, magnetic fields are produced in the rarefied gas of space, in theglowing heat of sunspots and in the molten core of the Earth. Such magnetismmust be produced by electric currents, but finding how those currents areproduced remains a major challenge.
Magnetic Field Lines
Michael Faraday, credited with fundamental discoveries on electricity andmagnetism (an electric unit is named 'Farad' in his honor), also proposed awidely used method for visualizing magnetic fields. Imagine a compass needlefreely suspended in three dimensions, near a magnet or an electrical current.We can trace in space (in our imagination, at least!) the lines one obtains whenone 'follows the direction of the compass needle.' Faraday called them lines offorce, but the term field lines is now in common use.Compass needles outlining field lines
Fi eld lines of a bar magnet are commonly illustrated by iron filings sprinkledon a sheet of paper held over a magnet. Similarly, field lines ofthe Earth start near the south pole of the Earth, curve around in space andconverge again near the north pole.
However, in the Earth's magnetosphere, currents also flow through space andmodify this pattern: on the side facing the Sun, field lines are compressedearthward, while on the night side they are pulled out into a very long 'tail,'like that of a comet. Near Earth, however, the lines remain very close to the'dipole pattern' of a bar magnet, so named because of its two poles.
To Faraday field lines were mainly a method of displaying the structure of themagnetic force. In space research, however, they have a much broadersignificance, because electrons and ions tend to stay attached to them, likebeads on a wire, even becoming trapped when conditions are right. Because ofthis attachment, they define an 'easy direction' in the rarefied gas of space,like the grain in a piece of wood, a direction in which ions and electrons, aswell as electric currents (and certain radio-type waves), can easily move; incontrast, motion from one line to another is more difficult.
A map of the magnetic field lines of the magnetosphere, like the one displayedabove (from a mathematical model of the field), tells at a glance how differentregions are linked and many other important properties.
Magnetism Definition
Electromagnetic Waves
Faraday not only viewed the space around a magnet as filled with field lines,but also developed an intuitive (and perhaps mystical) notion that such spacewas itself modified, even if it was a complete vacuum. His youngercontemporary, the great Scottish physicist James Clerk Maxwell, placed thisnotion on a firm mathematical footing, including in it electrical forces as wellas magnetic ones. Such a modified space is now known as an electromagneticfieldMagnetism Definition
.Today electromagnetic fields (and other types of field as well) are acornerstone of physics. Their basic equations, derived by Maxwell, suggestedthat they could undergo wave motion, spreading with the speed of light, andMaxwell correctly guessed that this actually was light and that light was in fact an electromagnetic wave.
Magnetism Meaning
Heinrich Hertz in Germany, soon afterwards, produced such waves by electricalmeans, in the first laboratory demonstration of radio waves. Nowadays a widevariety of such waves is known, from radio (very long waves, relatively low frequency) to microwaves,infra-red, visible light, ultra-violet, x-rays and gamma rays (very short waves, extremely high frequency).
Radio waves produced in our magnetosphere are often modified by theirenvironment and tell us about the particles trapped there. Other such waveshave been detected from the magnetospheres of distant planets, the Sun and thedistant universe. X-rays, too, are observed to come from such sources and are thesignatures of high-energy electrons there.