# Refraction of Light: Myth or Reality?

• Jaffer2020
In summary, the electric field of the electromagnetic wave exerts a force on the charged electrons of a medium, which in turn causes the electrons to oscillate and create their own electric field wave, creating a new slower net superimposed wave. This is why light slows down in a vacuum.
Jaffer2020 said:
Is the eigenfrequency just another term for the natural/resonant frequencies of some system, or is it different?
Yes, it's the resonant frequencies of the system.

hutchphd said:
Is Huygens Principle rubbish?
Has anyone suggested that it is? I can't see that the teacher was presenting any form of Huygens. There are a number of analogies to show how a wave front can change direction but they do not involve a 'reason' for change of wave speed - and neither does Huygens. In fact there are many theories from the past which are described, these days, in terms of what has been found out subsequently.

The term "rubbish" was applied to the wheel and axle explanation of the result of Huygens on the wave front. The speed change was a given at that point. It seemed to me a clever explanation but apparently was not admired by @Dr_Nate; I was questioninq both his analysis and his use of the word.

For the wave equation in 3 (spatial) dimensions the Huygens principle is correct. It's known as the regarded Green's function.

vanhees71 said:
For the wave equation in 3 (spatial) dimensions the Huygens principle is trtcorrect. It's known as the regarded Green's function.
I have to ask you at what age were you introduced to Green’s function and the maths of a wave function. How you would have dealt with it in tenth grade.
it’s a real potential failing of PF that contributions to virtually any thread are subjected to intellectual inflation and the ball is so often stolen from the OP.
How to present hard concepts at all levels is a very valid talking point. Perhaps the levels of posts should be policed stronger and the meaning of “off topic” could be re-examined.

This has come back from from an unexpected direction. I agree with both preceeding comments.
I thought the characterization of the teachers attempt to simplify the explanation (in a perfectly Huygens-reasonable way) as rubbish was unwarranted. Similarly Huygens is conceptually not that difficult and really is just a statement about the retarded Green's function.
My original complaint was I fact about my perception of intellectual snobbery (or snub-ery)

hutchphd said:
My original complaint was I fact about my perception of intellectual snobbery (or snub-ery)
Oh yes, there is plenty of that about but there is another aspect of 'telling people about things' and that is age appropriateness. There would be no point in trying to explain a phenomenon to a five year old in terms of maths or even 'Science reasoning'. It's not being snobbish to limit ones reaction to a young child's question to 1. Confirming that what they saw is what we all see and 2. Describing similar examples in other contexts, perhaps giving it a name for future reference.
Story: I was walking down our back lane with my little granddaughter (hah - those were the days!) in the late afternoon and the Sun was low in the sky, the other side of a sparse hedge. She excitedly remarked that the Sun was following us. Should I have told her about the geometry of parallax? That would have brought the shutter down for another couple of years. I simply pointed out that distant trees were doing the same thing and that it was all to do with distance and waved my arms about a bit. In her case, there is another factor. She has rather serious strabismus and it is doubtful whether introducing binocular vision would have helped - so I didn't. Did she miss out in any way, from my reaction?

hutchphd

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