Category: physics

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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lab –> www

A lab is a place where questions are asked, experiments are conducted, and theories are tested…& sometimes.. in this pursuit, the world is changed.

A case in point is the connection between CERN and the origins of www :

https://home.cern/science/computing/the-birth-of-the-web

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Tiny value of the radiation pressure of sunlight on Earth

 

  • If radiation pressure is indeed a genuine electromagnetic phenomenon, then why don’t we observe it in our everyday lives?
  • The reason is that the magnitude of the radiation pressure from the natural light source on Earth (the Sun) is feeble.
  • from electromagnetic theory, this tiny amount of pressure can be calculated by the formula \(\frac{E}{c}\), where ‘E’ is the energy of sunlight on earth and ‘c’ is the speed of light in vaccum (which is \(3 \times 10^8 \text{ ms}^{-1}\) [\(9.83 \times 10^8 \text{ ft s}^{-1}\)]).
  • Maxwell himself recognized the low value of this energy, which he assumed to be \(83.4 \frac{\text{ft} \cdot \text{pound}}{\text{sec} \cdot (\text{ft})^2}\)
  • Taking this value and dividing it by ‘c’ gives us a radiation pressure of \(10^{-7} \frac{\text{pound}}{(\text{ft})^2}\).
  • Poynting, who extensively worked on radiation pressure from an electromagnetic theory viewpoint, compared this tiny pressure to the size of a grain in an area of \(200,0000 \text{ (ft)}^2\)!
  • This highlights why radiation pressure is hard to measure experimentally, and it took some trial and error to ascertain the value and the method. More on this later…

Reference :

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.

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When Chandra’s paper got rejected

Sometimes, referee reports can be frustrating, especially if your paper gets rejected and criticized without justification. This is not a new thing in scientific discourse, and even accomplished researchers like S. Chandrasekhar had to face such rejections. As Chandra notes in the winter of 1956:

“The frustration of these months was due also to the fact that the Royal Society rejected my second paper on turbulence with a most discourteous referee’s report. I withdrew the paper, but continued the correspondence with the referee. The referee withdrew some of his more blatant remarks; but the whole incident was an unhappy interlude. I went specially to Washington to talk to von Neumann; and corresponded also with Heisenberg.” (Chandrasekhar, 2010, p. 38)

When a paper gets rejected, what is important is to seek feedback from people who are knowledgeable and courteous. Chandra had friends such as von Neumann and Heisenberg to seek input. One cannot get better than this.  

Source:  Chandrasekhar, S. 2010. A Scientific Autobiography: S. Chandrasekhar: With Selected Correspondence. (posthumously published)

Chandra quotes Virginia Woolf

The well-known astrophysicist, S. Chandrasekhar, liked the writings of Virgina Woolf. In her words, he found a unique channel to philosophize his own work, as he did in 1957:

‘By accident, I found the following quotation from Virginia Wolff (Woolf) which expressed very accurately my attitude to my work of the past years. This quotation ends my Rumford Lecture.

“There is a square. There is an oblong. The players take the square and place it upon the oblong. They place it very accurately. They make a perfect dwelling place. The structure is now visible. What was inchoate is here stated. We are not so various or so mean. We have made oblongs and stood them upon squares. This is our triumph. This is our consolation.”’ (Chandrasekhar, 2010, p. 41)

Source:  Chandrasekhar, S. 2010. A Scientific Autobiography: S. Chandrasekhar: With Selected Correspondence. (posthumously published)

Note: The source spells Woolf as Wolff

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