Letters
Faraday discovered crosstalk! What happened to the Electromagnetic Theory?
O
n 21 April 1820, during a lecture, Ørsted noticed a compass needle deflected from magnetic north when an electric current was nearby.
Faraday’s breakthrough came when he
wrapped two insulated coils of wire around an iron ring, and found that, upon passing a current through one coil, a momentary current was induced in the other coil. (Or did he drop a magnet through a coil, now to be seen in the Science Museum?) Tis phenomenon is now known as
mutual induction. Published in 1831. Or was it a current that passed through one coil, and what exactly was induced in the other coil. Was it electric current? Tis question was not asked for the next 200 years. Tis second discovery closed the loop in
an elegant way. Electricity caused magnetism, which caused electricity. But did it? Regarding Faraday, consider a single turn
transformer; see Figure 1. When the switch to the battery to the leſt
is closed, a voltage/current step advances towards the transformer at the speed of light, as shown in Figure 3. Tere are four factors which make up
the wave; see Figure 2: • Electric current in the conductors i; • Magnetic field, or flux, surrounding the conductors B;
• Electric charge on the surface of the conductors +q and -q;
• Electric field, or flux, in the vacuum terminating on the charge, D. Reaching the transformer, some of it
continues on its journey at the reduced speed 1/√µƐ for the magnetic material. Some of this transverse electromagnetic wave leaks out into the secondary, continuing to travel at the 1/√µƐ, as discussed in my article in Electronics World in January 2011. When the energy reaches the right-hand end of the transformer, some of the TEM wave proceeds further to the right and some reflects. Te TEM wave proceeding further to the right reached Faraday’s galvanometer, which could only measure electric current and failed to detect the accompanying magnetic field. At every stage, only TEM waves, made up of electric and magnetic field E x H, were involved. At no stage was there isolated electricity E or isolated magnetism H. Electricity did not cause magnetism, magnetism did not cause electricity. At every stage, a TEM wave was involved, causing further TEM waves. In 1861, Maxwell paved the way for the
alleged causal link between electricity and magnetism in Maxwell’s Equations. However, selections from his chaotic “A Treatise on Electricity and Magnetism” at http://www.
ivorcatt.co.uk/x892max.pdf show that he did not think so. Because of Faraday’s alleged earlier “discovery” of electromagnetic induction, these equations are taken by everyone to imply causality, with E causing H causing E further away. However, as my
co-author Dr David Walton points out, Maxwell’s mathematics does not do so. It merely describes the relationship between E and H in a TEM wave, which is one of fixed proportion. In Maxwell’s book, page 439 of volume
2 has a diagram with sinusoidal E and H in phase, and so not causing each other. Page 440 has half of the energy in the electric field and half in the magnetic field. (Te Wakefield experiments show that this
is nonsense, with E and H energies suddenly morphing into all E energy; see http://www.
ivorcatt.co.uk/x343.pdf . All the energy is always in the single E x H.) Maxwell’s Equations for a TEM wave were
cleaned up by Heaviside and rewritten: δE/δx = - δB/δt δH/δx = - δD/δt Tey are taken to indicate causality. Not
surprisingly, the equally valid equation δE/δx = -Zo
Ɛo δE/δt, which I published
in Electronics World in November 1985 (
http://www.ivorcatt.co.uk/x18j184.pdf), is overlooked. Tese last equations tell us that E causes E! If E causes itself, does it really cause H in the same way? When addressing a sinusoidal TEM
wave travelling at the speed of light guided by two conductors, a lecturer will tell you that a changing E causes H, and a changing H causes E further along. No text book or lecturer will tell you that E and H are in phase, and perhaps they do not know this. Properly read, the first two formulae above tell you that changing E correlates with changing H. If one caused the other, we would expect to see something like δD/ δt = B or – B (displacement current causes magnetism), but that is not what we see. All lecturers and text-book writers, versed
Figure 1: Single turn transformer
in the history of the subject, knowing of the discoveries of Ørsted and Faraday, “know” that E causes H, which causes E. Tis was fine for analogue radio and even radar, when sine waves were the only signals, and there was always a changing E and a changing H, so long as their relative phase was unknown
62 December/January 2021
www.electronicsworld.co.uk
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