Session 6 Magnetism, starting with MAGNETOSTATICS


Most physics courses up to the 1950's did contain a considerable amount of material relating to mangnetism. Magnetic fields could easily be displayed by the patterns formed with iron filings or an array of compass needles and the earth's magnetic field was well documented. Compared with electrostatics (session 3) where the humidity of the Laboratory played a crucial role as to "how well the experiment worked out", a magnetic experiment was well behaved. The fact that we tend to regard magnetostatics and electrostatics as separate entities is, in some way, accidental and stems from the fact that the subjects arose from the discovery of two minerals, amber and lodestone, whose properties were studied separately. That these two subjects bear a certain formal resemblance to each other is of little significance when we realize that whereas electric charges exist, magnetic poles do not. Indeed, this formal resemblance probably retarded the discovery of the true connection between electricity and magnetism, which is rightly regarded as one of the greatest achievements of nineteenth-century physics, namely, the formulation of ELECTROMAGNETISM.

The concept of magnetic poles is undoubtedly a useful one and, in following the historical development of the subject of magnetism, students may find it useful to devote some time to the concept of free poles. Also, at the back of one's mind the concept of monopoles lingers and, in Ryder's article "Charge" in Physics Education, 2007, vol 42(2), page 145 we see that a theoretical formulation does predict the presence of free poles.

To put the subject into historical context one may wish to follow the "timeline" given by MAGCRAFT:

The web connection is given below

A typical calculation that students would carry out in their initial studies of magnetism is to find the magnetic field intensity due to a bar magnet:-

As with the case of the Electrostatics session 3 , there are software simulations and Colorado University has offered a field plotter for bar magnets. It also includes a plot of the Earth's magnetic field :


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