magnetic field

2004 18:53:21 -0400,


I like this one:
A physical property of an object that shows attraction for iron, as in a magnet. Electromagnetism acts between particles with an electric charge, such as electrons, protons, and ions. It is believed to be associated with moving electricity, and it creates fields of force.
http://helios.gsfc.nasa.gov/gloss_mn.html
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I doubt if Maxwell's Equations can be simplified. They are elegantly simple by themselves.
However... for a layman, you may assume that anywhere there is a changing (alternating) magnetic field, in a conductive medium, their will be an associated alternating electric field that goes along with it.
There are many practical examples where these fields may be observed, calculated and measured.
1. AC Power Lines - If you could see the magnetic lines of force, you would see a concentric circle projected from the radius of the power line increase in size as the current increases, the circle would reverse direction at the instant of maximum current flow and as the current decreases... ultimately collapsing to zero as the current goes through the zero crossing. The polarity (direction) of the circular magnetic lines of force reverses in step with the reverse of current flow in the conductor. There are simple meters that can measure both dynamic AC and static DC electromagnetic fields.
The electric field lines of force shoot our radially in all directions from an energized power line with an intensity dependant upon the voltage of the line. The electric field typically exends all the way to the ground. Insulators are designed to concentrate this voltage gradient over a fixed number of elements, thus allowing a grounded structure such as a support pylon to be brought within a few feet of the conductive cable.
2. Radio antennas always have a magnetic field component and and an electric field associated with them.
3. All visible light, radio, x-rays, infrared, UV energy etc. is composed of electro-magnetic radio waves of varying frequency. Air or space is considered a conductive medium in this case.
Beachcomber
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--------------- actually- for most lines- except an isolated conductor which doesn't exist, this is not true. The field produced is due to the effects of all current carrying conductors. The resultant, at any point is directional and the horizontal and vertical components are not necessarily a maximum at the same time. Care must be taken with simple meters as they often will not give the whole picture.

---------- Again - insulators do not concentrate the field- they are used in regions of high field and co-ordination of the insulators with the air gaps is important. Also, as with the magnetic field- all sources contribute so a simple visualisation of circular equipotentials and radial lines of flux is simplistic except for the non-existant case of an isolated single conductor.
In any case the original question was with respect to what is a magnetic field. A proper answer to this has been given - it is simply a region where magnetic effects can be seen. Why the effects occur or what is magnetism is not germane to the issue.
--
Don Kelly
snipped-for-privacy@peeshaw.ca
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I can give you my point of view:scientists (and applied science) always looks *the use* of certain inventions, and not in-depth-view of what magnetic field is really.So, you have a rotating magnet inside a stator:voila, an alternator. You have a stator that creates a rotating magnetic field and inside it a "squirrel cage" rotor:voila, an asynchronous rotor.Without both the inventions, todays world would not exist. Imagine a refrigerator motor with brushes.Or a fan motor with them.Or generating electricity only with DC.Actually, the equations of Maxwell, describe an electromagnetic field, used to transmit TV and radio, and have nothing to do with pure magnetism (even in the more complex form of the rotating magnetic field).The magnetism...is something.
-- Dimitris Tzortzakakis,Iraklion Crete,Greece major in electrical engineering freelance electrician dimtzort AT otenet DOT gr

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