The concept of “ free space “ may be visually appealing to the senses, but this perception very rarely ( if ever ) describes any meaningful description of any region of space. This argument can easily be confirmed with objects as simple as paper clips and refrigerator magnets. Under the right conditions, seemingly magical forces make themselves manifest without the usual mass-to-mass interactions more familiar to the five senses. A sophisticated description of electromagnetic theory requires studies beyond those found in introductory textbooks; however, students must begin studying these topics at some point, so a simplification of advanced electromagnetic theory is provided herein. We’ll begin our studies with a diagram of a simple bar magnet:
Our naked eyes see this model as being naked, but this hunk of metal has within it countless tiny bar magnets called electrons. By melting metal and placing it within a strong magnetic field, the magnetic fields of its electrons align, and when the metal cools, these electrons are relatively “ fixed “ in space and orientation. These small particles possess angular momentum that is quantized. More importantly, the magnetic fields of these electrons cooperate in a way that causes the macroscopic metal object to itself become a bar magnet:
In spite of the nobility of my efforts, the lattermost diagram still does little justice in describing the nature of field lines that engulf a magnet. In reality, the magnetic field lines do not terminate at the north and south poles. Rather, the field lines can be diagrammed as concentric loops that never lose connectivity. The actual field lines that align with the magnet are much, much more numerous than indicated in any simple diagram. Also notable is the fact that magnetic field lines never, ever cross one another.
For the moment, it is practical to accept some rudimentary facts as being validated by observation, experiment, and repetition without any rigorous mathematical derivations. The field lines above are called magnetic flux ( ɸ ), and the unit of magnetic flux is the weber ( Wb ). One weber of magnetic flux contains an incredible 108 field lines!!! It is sometimes more practical to use a fraction of a weber to simplify making measurements, and for this reason, the microweber ( µ Wb ) consisting of 100 magnetic field lines is used.
The next concept of importance regards how much magnetic flux lines penetrate any given imaginary area in space. This is analogous to making sense of the number of moles ( mol ) of substance that exist per liter ( L ) of an atomic or molecular substance ( M ). Not to be distracted, however, the concentration of flux per unit area is called the magnetic flux density ( B ). The flux lines in question are exactly perpendicular to the area in question. The SI unit of magnetic flux is the Telsa ( T ), and its measured in units of webers per square meter ( Wb / m2 ):
B = ( ɸ / A )
As a final note, the magnetic flux around a magnetic object can be manipulated to act in a similar fashion to an electric current moving through a wire that has been bent into a particular shape. For example, a metallic object placed beside a magnet provides a better path for magnetic lines of force to pass than the surrounding air medium. This makes certain types of metals and other materials crucial components of shields that protect sensitive circuits from stray magnetic fields:
RENAISSANCE PHYSICS 