Draft:Hertz’s experiments on electromagnetic wave

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  • Comment: Many of these sources are very old - that is, they are primary sources, or very close to it. Please use secondary sources wherever possible, especially when you're saying things like "it is interesting that", ie, putting a claim in "wikivoice". It's fine to use primary sources for simple statements of fact ("he published his results in 1888", "he described the experiment as "blah blah"", etc). asilvering (talk) 07:08, 24 April 2024 (UTC)

Reply to @Ozzie10aaaa: Thank you for the comment. I agree some parts of it were mentioned in the article on “Heinrich Hertz”. However, this is a very important experiment in the history of science. According to Professor M. S. Longair of Cambridge University, Hertz’s experiment on EM waves was “the final proof of the validity of Maxwell’s equations”; “Maxwell died in 1879 before direct experimental evidence was obtained…The matter was finally laid to rest ten years after his death in a classical series of experiments by Hertz”.[1] Because of its importance, I think the Hertz’s experiment on EM waves should worth a dedicated article.

Hertz’s conducted a series of experiments on EM waves. In the current article of Hertz’s experiment on EM waves, I focused on the most well-known experiment on the first clear demonstration of the EM waves propagation in air (The one published in 1888). The historical background for this experiment was briefly introduced. The experimental setup was described and a new figure on experimental setup was added for easier understanding. Of course, further improvement is needed. The content in Heinrich Hertz page and this experiment page can be edited further to supplement each other: the former focusing on the man and his general contribution to science, while the latter focusing on this particularly important experiments conducted by Hertz. They could be good cross-referencing pages. Spinecho001 (talk) 07:18, 29 February 2024 (UTC)

Electric Waves by Hertz
Electric Waves, a collection of work by Hertz

A series of well-known experiments conducted by Heinrich Hertz starting from 1887, which generated and detected the electromagnetic waves, and examined wave properties of EM waves such as interference and reflection[2]. The experiments gave clear demonstration of the wave properties of the electromagnetic waves which was predicted by Maxwell in his theory of electricity and magnetism. The Hertz's experiment was considered the final proof of the Maxwell's theory which unified electromagnetic waves and light. [1]

Background[edit]

Faraday first proposed the concept of "lines of force". Following Faraday's concept, Maxwell published a series of papers under the title of On Physical Lines of Force. One of them derived the speed of light c from the expression of the velocity of the electromagnetic wave in relation to the vacuum constants. In 1865, Maxwell published A Dynamical Theory of the Electromagnetic Field, with Maxwell's equations in its final form. In 1873, Maxwell wrote A Treatise on Electricity and Magnetism which gave his full theory. The Maxwell's theory predicted that the electromagnetic waves are the same as light waves. They both propagate in the same finite speed. The theory also gave the same wave equation for electromagnetic wave propagation and light. [3] Unfortunately, Maxwell died in 1879, before any direct evidence came out for his predictions.

Physicists actively worked on the generation of electric magnetic waves from an electric source. Among them, Oliver Lodge and G. F. FitzGerald were well known. However, these experiments were not successful.[4]

Another key question at that time was what is the carrying medium for such electromagnetic waves. From the Newtonian view, the vacuum is an empty space. Forces, such as gravitational force, should be able to act-at-a-distance instantly. Maxwell believed that the electromagnetic waves propagates through a medium pre-filling the space called ether. The electric force thus also was transmitted through this ether medium. Physicist at that time were interested to test if the speed of the electric force is finite or infinite; and whether there was an ether medium in space. [2]

Maxwell's work on electromagnetism was translated by Helmholtz to German. Hertz was a student of Helmholtz, he was well familiar with the Maxwell's EM theory. Starting from 1887, Hertz experimented various setups for finding relationships of electromagnetic forces and dielectric polarizations. He also aimed to determine if the electric force propagate with a finite or infinite speed.[2] It is interesting that Hertz's discovery of the electromagnetic waves propagating in space was a serendipity. [5]

Hertz's Experimental Setup[edit]

In his experiment clearly demonstrating the generation and detection of electromagnetic waves, Hertz used a resistor-inductor-capacitor circuit and connected it to a loop of wire with a gap to generate the EM waves.[6] The capacitors Hertz used were two This circuit was called the primary circuit. When the capacitors were charged up, high voltages induced in the gap produced sparks that were visible to naked eyes. This is clear evidence of the generation of the EM waves. The receiving device was another loop of wire with a gap placed across the room (as far as 12 meters away) so that it was away from the source circuit. The gaps can be adjusted. Hertz called the receiving device "resonator". After the primary circuit was charged, the sparks were also seen in the gap of the detecting device. It showed that the EM waves generated can travel in the air across the room to reach the detecting device. The electromagnetic wave generated by the experiment was called "Hertzian wave" after Hertz. Later, people realized the EM waves generated in Hertz experiments was actually the radio waves.[citation needed]

The Figure of experimental setup shown in Hertz's paper in 1888. A, A' are two metal plates of 40cm in the side, used as the capacitors. They are connected by wire with a gap in the middle. When the AA' are charged up through the induction coil J, the high voltage will produce sparks in the gap. Thus it generates electromagnetic waves. This part of the experimental setup can be seen as the radio wave transmitter. Source: Electric Waves

Hertz also conducted experiments on the reflection, refraction, and interference patterns of electromagnetic waves, confirming their wave characteristics.[7][8]

At that time, there were debates if the propagation of electric force is instant or with a finite speed. Thus, Hertz worked on determining the speed of EM waves is finite or not. Hertz determined the wavelengths from the interference patterns, and by estimating their frequencies, he calculated the propagation speed of EM waves. The experiment clearly showed the finite propagation speed of EM force. Furthermore, by comparing the speed of the EM wave and that of light, he supported Maxwell's theory on the unification of electromagnetic waves and light.[6][9]

The Maxwell equations presented in the volume of A Treatise on Electricity and Magnetism was hard to understand.[2] It was not widely read. It was believed that Hertz experiments on generation and detection of the electromagnetic waves greatly contributed to the acceptance of the Maxwell's theory on electromagnetism.[4]

Wikisource has original text related to this article:

The publication of of Hertz's research work on electromagnetism were collected and translated to English into three volumes: Electric Waves, Miscellaneous Papers and The Principle of Mechanics. [2]

Application[edit]

Main article: History of radio

Hertz's experiment was not aimed to generate applications for practical use. However, his experiments in generating and detecting EM waves (radio waves) became the basis for future development of the radio technology.

See also[edit]

External Link[edit]

A modern demonstration of Hertz' experiment on EM waves YouTube video: https://www.youtube.com/watch?v=9gDFll6Ge7g

References[edit]

  1. ^ a b Longair, Malcolm (1984). Theoretical concepts in physics: an alternative view of theoretical reasoning in physics for final-year undergraduates. Cambridge: Cambridge Univ. Pr. pp. 49–51. ISBN 978-0-521-25550-9.
  2. ^ a b c d e Watson, E. C. (1957-09-01). "On the Relations between Light and Electricity". American Journal of Physics. 25 (6): 335–343. doi:10.1119/1.1934460. ISSN 0002-9505.
  3. ^ A Treatise on Electricity and Magnetism.
  4. ^ a b Flood, Raymond; McCartney, Mark; Whitaker, Andrew, eds. (2014). James Clerk Maxwell: perspectives on his life and work (1st ed.). Oxford New York, NY: Oxford University Press. ISBN 978-0-19-966437-5.
  5. ^ The Preface written by Lord Kelvin in Electric Waves
  6. ^ a b Hertz, Heinrich (1888). "ON THE FINITE VELOCITY OF PROPAGATION OF ELECTROMAGNETIC ACTIONS". Wiedemann's Ann. 34.
  7. ^ "Generating Electromagnetic Radiations - Concept | Physics | JoVe". app.jove.com. Retrieved 2024-02-27.
  8. ^ Hertz, Heinrich (1893). Electric Waves. Translated by Jones, D. E. New York: Macmillan.
  9. ^ Maxwell, James C. (1861). "On Physical Lines of Force". Philosophical Magazine.

Category:History of physics

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