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Dec. 20, 2005 As I mentioned in Part 1, the simplest form of one of Maxwell’s famous equations is: B* = M H*, where I have used B* to denote the magnetic flux density, measured in Teslas (T), M (for Greek mu) to denote the magnetic permeability of the medium, measured in Newtons per ampere squared (N / A^2), and H* to denote the magnetic field strength, measured in Amperes per meter (A / m). The asterisks signify that the quantities so marked are vectors, and necessarily have a direction. If we assume, for example, that H* is directed northwest, then B* also will be directed northwest, at least in what has been discussed so far. I have said that M is a scalar, in other words, the product of a simple number and a compound unit of measure. A vector multiplied by a scalar is simply another vector in the same direction. An easy analogy would be the case of a car going 30 mph northwest, which we call V1*. I tell you to triple the velocity. Now you are going 90 mph northwest, which we call V2*. Then we can say V2* = 3 x V1*, where the multiplier 3 in no way signifies a change in direction. For M to be a scalar, as we have thus far assumed, the medium must be isotropic. In other words, it must exhibit the same magnetic permeability in all directions, as would be the case with vacuum, air, pure iron and most other materials. But there may be materials, called anisotropic, that deflect the direction of the vector, much as a ray of light is diffracted when it strikes a thick piece of glass. Then M will no longer be a scalar, but instead will be a second-rank tensor, which would appear in italics or with some other special notation. Let me just use M#, which usually takes the form of a 3 x 3 matrix. So we would have: B* = M# H*. The presence of the second-rank tensor tells us immediately that B* and H* are in different directions. M, the permeability of the medium, is the product of relative permeability and free-space permeability: M = Mr x Mo. Permalloy has a relative permeability of 8000. That means simply that it is 8000 times as good a magnetic medium as vacuum. The permeability of free space or vacuum is equal to 4 pi x 10^-7 N / A^2, so the permeability of permalloy is 32,000 pi x 10^-7 N / A^2, or .01005 N / A^2. So given an equal H* or magnetic field strength, a magnet made out of permalloy would be 8000 times as good a magnet as vacuum, with 8000 times the magnetic flux density, B*. So who is so terribly interested in magnets anyway? As I mentioned in Part I, an electrical charge moving relative to a magnetic field undergoes a force. Consequently, a material with a lot of free electrons, like copper, will undergo an electron flow, carrying energy, if moved in a magnetic field. This flow of electrons constitutes what we call electricity. Another phenomenon is that the current generated in a conductor can be multiplied by looping the conductor about an armature. So if I have 1000 loops moving in the field, I generate 1000 times as much electricity. So in a power plant, the turbines move an armature wound with a conductor between the poles of a powerful magnet to make electricity. The motion is relative, however. The magnets may be moved while the armature remains still. The quantity of the electricity generated is measured in Amperes (A), which amount to Coulombs per second (C / s), and the energy is measured in Volts (V), which amount to Joules per Coulomb (J / C). There is more to the subject of magnetic permeability, though, but let me defer that to Part 3. ------------ About the author Thomas Keyes: I have written two books: A SOJOURN IN ASIA (non-fiction) and A TALE OF UNG (fiction), neither published so far. I have studied languages for years and traveled extensively on five continents. Email: udikeyes@yahoo.com Tell a friend about this site! ------------ All articles are EXCLUSIVE to Useless-Knowledge.com and are not allowed to be posted on other websites. ARTICLE THIEVES WILL BE PROSECUTED! |
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