Letters


Voltage, current, charge and photons T


he reasoning presented in the letter ‘Faraday discovered crosstalk’ in the December/January 2021 issue of Electronics World is puzzling in the


extreme. Ivor Catt uses the relationships of Electromagnetic Theory to make his various points, yet pours scorn of those self-same relationships! For example, he states: ‘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 this energy in the electric field and half in the magnetic field. The Wakefield experiment shows that this is nonsense...’ Later on, he states: ‘no textbook


or lecturer will tell you that E and H are in phase, and perhaps they do not know this’ yet goes on the introduce a couple of diagrams of the transverse electromagnetic (TEM) wave. This waveform depends on the fact that voltage V and current I are in phase, and this can only happen if the electric field E and the magnetic field H are in phase. One of the concluding statements is


‘ ... I believe that the causality relations alleged to reside in Maxwell’s equation (i.e. changing magnetic field producing electric field and changing electric field producing magnetic field ) are spurious’.


Current, voltage and charge If it is accepted that both voltage and current are manifestations of moving charges, then there is no need to invoke


the concept of ‘causality’. They are both functions of the same entity. The article ‘Updating Circuit Theory: Charges and Photons’ on the EW website shows how the propagation of charges back and forth along a transmission line relate to the distribution of voltage and current along the line.


Electric field The use of time-step analysis can be developed further to simulate the behaviour of a test rig when a step pulse is applied to a line which is open- circuited at the far end. See ‘Updating Circuit Theory: Transient Emissions’. Reflections will create a square wave which morphs into a sine wave and decreases in amplitude until the oscillations are undetectable. Under steady-state conditions there will be positive charges on the surface of the send conductor and negative charges on the surface of the return conductor. This state is sustained by photons which propagate to and fro between the conductors. (It is a bit like a swan gliding gracefully over the water. What is not visible is the furious paddling that goes on under the surface.)


Magnetic field If a step voltage is applied to a cable which is short-circuited at the far end, then the current will increase in the form of a series of steps. At every step, the number of photons being interchanged between the conductors will increase.


The amplitude of the current will increase exponentially, limited only by the resistance in the circuit. Te stored energy due to the flow


of charges can be likened to that of a flywheel which is gradually speeding up, or to a train leaving the station. Tis stored energy is sustained by the vastly increased number of photons propagating to and fro between the conductors. The article ‘Updating Circuit Theory:


Transient Cross Coupling’ in the Electronics World website illustrates this interaction.


Conclusion As far as Transmission Line Theory is concerned, voltage and current are manifestations of moving charges. These charges appear to flow to and fro between the conductors as well as back and forth along the conductors. This can be explained by invoking the


relationships of Quantum Theory. The real energy carriers are photons. These are the entities that propagate to and fro, creating charges on the surfaces of the conductors and causing electrons to surge forward and back along those conductors. It is possible to agree with one statement


by Ivor: ‘No mechanism invoking E producing H and H, in return, producing E is required.’ Both are functions of the same entity: the photon.


Ian Darney 2 March 2021


IN THE JUNE ISSUE OF ELECTRONICS WORLD MAGAZINE: Special reports include:


Medical design • Embedded design • Communications systems • Aerospace • Development boards • Semiconductors


There are also the usual regular columns, focusing on embedded design, software, interfaces, and green and sustainable electronics, as well as a brand new section called Circuit Drill, which covers circuit analysis and troubleshooting at the workbench. Not to miss out, subscribe by contacting data@datateam.co.uk. More information and technical material is available on the Electronics World website at


www.electronicsworld.co.uk 18 May 2021 www.electronicsworld.co.uk


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