Tag: electromagnetism

The 5 Maxwellians

One of the underappreciated facts is the amount of work that people did to bring Maxwell’s theory of electromagnetism to the form that we use today. Among many enthusiastic researchers, five names often come into the picture, and they are Poynting, Heaviside, Fitzgerald, Lodge, and Hertz. Without their contribution, we would have been seeing a very different form of Maxwell’s electromagnetic theory and the equations named after Maxwell. As Loudon and Baxter describe: “The main influence on all of the activity in electromagnetic theory during the later years of the nineteenth century came from Maxwell’s famous treatise (Maxwell 1873). Poynting was a member of the group of young physicists led by Heaviside, Fitzgerald, Lodge and Hertz who developed Maxwell’s electromagnetic theory in the years following his death in 1879. They transformed his 1873 presentation into the formalism recognizable today as Maxwell’s equations.” (Loudon and Baxter, 2012, p. 1826)

Interestingly, all five Maxwellians were not only interested in electromagnetic field theory but also applied it to a variety of practical problems. Poynting wrote an elaborate paper in which he describes the transfer of energy and momentum of electromagnetic waves titled “On the Transfer of Energy in the Electromagnetic Field” (Poynting, 1884, p. 343), and connected them to a series of interesting observations in electromagnetism. Among the seven applications Poynting discussed in his paper, the last one was on the theory of electromagnetic waves, and it is there that he computed the maximum value of the velocity of light. More on this in a future blog.

References:

Loudon, R., and C. Baxter. ‘Contributions of John Henry Poynting to the Understanding of Radiation Pressure’. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 468, no. 2143 (2012): 1825–38. https://doi.org/10.1098/rspa.2011.0573.

Poynting, J. H. ‘XV. On the Transfer of Energy in the Electromagnetic Field’. Philosophical Transactions of the Royal Society of London, no. 175 (December 1884): 343–61. https://doi.org/10.1098/rstl.1884.0016.

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Light as EM wave – in Maxwell’s words

Every year, I teach an optics course to physics majors (including physics iPhD students and MS Quantum Tech students). In the process of introduction, I discuss how light was discovered to be an electromagnetic wave. One of the thrills of this topic is to quote Maxwell from his legendary 1865 paper1, in which he makes this monumental connection. Every time I teach this, I get an intellectual kick, even after doing this for almost 1.5 decades.

The highlighted text is the famous statement. Before that, Maxwell compares his result with two experimental results and confirms his prediction. I follow this up with Hertz’s experiment.

Note: Electric waves and telegraphy were already known before Maxwell’s paper. There were papers that discussed about velocity of light and its connection to electric waves. See this paper2, for example. However, these interpretations were not as comprehensive as Maxwell’s case, and importantly, the field theory viewpoint needed Faraday’s experiments and Maxwell’s interpretation.

  1. Maxwell, James Clerk. 1865. “VIII. A Dynamical Theory of the Electromagnetic Field.” Philosophical Transactions of the Royal Society of London 155 (January): 459–512. https://doi.org/10.1098/rstl.1865.0008.
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  2. https://www.ifi.unicamp.br/~assis/Weber-Kohlrausch(2003).pdf ↩︎