Evidences of the electromagnetic nature of light

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Discussion Overview

The discussion revolves around the evidences supporting the electromagnetic nature of light, exploring historical, theoretical, and experimental perspectives. Participants consider various types of evidence, including the oldest, simplest, and most convincing examples, as well as the historical context of Maxwell's contributions to the understanding of light as an electromagnetic phenomenon.

Discussion Character

  • Exploratory
  • Historical
  • Debate/contested

Main Points Raised

  • Some participants suggest that Maxwell's derivation of a wave equation for electromagnetic fields, which matched the speed of light, serves as a historically convincing argument for the electromagnetic nature of light.
  • Others argue that while the speed of light was a significant finding, it may be viewed today as a more general constraint rather than solely an electromagnetic characteristic.
  • One participant highlights Faraday's early work with the Faraday effect, which demonstrated the rotation of the plane of polarization of light in a magnetic field, suggesting it as an early indication of light's electromagnetic properties.
  • Another participant notes that while the Faraday effect supports the idea of light being a transverse wave, it does not definitively prove it to be an electromagnetic wave, indicating a nuanced view on the interpretation of this evidence.

Areas of Agreement / Disagreement

Participants express differing views on the strength and implications of historical evidence regarding the electromagnetic nature of light. There is no consensus on which evidence is the most convincing or how to interpret the significance of early findings.

Contextual Notes

Some arguments depend on the interpretation of historical evidence and the definitions of electromagnetic phenomena, which may not be universally agreed upon. The discussion reflects a range of perspectives on the implications of Maxwell's equations and Faraday's experiments.

lalbatros
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Hello,

I could give many arguments supporting the electromagnetic nature of light.
The whole net of modern physics can be used for that, specially atomic physics.

However, I wonder what could be the best evidences like:

- the oldest
- the simplest
- the most convincing
- the cheapest (in a lab)
- the most clever
- ...

In addition, as was asked in another thread, I would be curious to know how this idea came to Maxwell.
Is it simply the matching of the velocity of light with the Maxwell's equations?
Did the people at that time already have some suspicion?

Thanks,

Michel
 
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Historically, the most convincing is probably Maxwell deriving a wave equation for EM fields and finding that the velocity of the wave is equal to 1/sqrt(epsilon_0*mu_0) = c, that is the speed of light (an optical phenomenon) can be described in terms of electromagnetic constants (epsilon_0 and mu_0).

Claude.
 
It is true that in these old times, the speed of light could be considered like a fingerprint.
Today, this evidence would be less convincing ... even with many more decimals on the speed of light. We would tend to think of c as being more general than electromagnetism, a constraint put on the speed of light and any other speed.
 
The earliest idea that light might be an EM phenomenon was by Faraday who rotated the plane of polarization of light with a magnetic field.
Put "Faraday effect" into google.
 
Thanks clem, this is a very nice example.

I should have thought to it.
I knew the Faraday rotation is used in Tokamaks to measure the current distribution.
The total rotation is measured along several chords.
This allows a mathematical reconstruction of the current flowing through the plasma (in real time!).

I will try to find more about the original Faraday experiment.
 
clem said:
The earliest idea that light might be an EM phenomenon was by Faraday who rotated the plane of polarization of light with a magnetic field.
Put "Faraday effect" into google.

This would prove light to be a transverse wave; but not necessarily an EM wave.

But that it just my nitpicky opinion!

Claude.
 

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