Evidences of the electromagnetic nature of light

[lalbatros]

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

 

[Claude Bile]

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.

 

[lalbatros]

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.

 

[Meir Achuz]

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.

 

[lalbatros]

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.

 

[Claude Bile]

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.