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.
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
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.
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
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
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.
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
dimtzort AT otenet DOT gr
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