Good observation, but I don't think the angle of the light source is great
enough to account for the number of helical turns within the
given length of the tube.


On Thu, Sep 21, 2023 at 6:20 PM MSF <> wrote:

> One other thing. If you aim a laser into the inside of a transparent tube,
> you get that barber pole effect spiraling around at a greater or lesser
> frequency depending on the angle of the beam into the interior of the tube.
> So that may explain the barber pole in the video.
> ------- Original Message -------
> On Thursday, September 21st, 2023 at 9:05 PM, MSF <
>> wrote:
> I can't even begin to express how conceptually and experimentally wrong
> this demonstration is. The first thing is the perpetuation of the mistaken
> idea that photons are wiggling in a sinusiodal fashion. When you see that
> sine wave, it's a graph of the varying field as the wave propagates. It's
> not the wave itself. This is such a common miscommunication that physics
> students often have a hard time getting over it.
> Just for the sake of context, this guy should have at least mentioned the
> practical application of this phenomenon, which is the polarizing
> saccharimeter. Wine makers, for example, use this device to measure the
> amount of dextrose (glucose) in grape juice so they can harvest the grapes
> at their peak. So next time you're enjoying that glass of wine, think,
> "Mmm...saccharimeter."
> The experimental setup in this demonstration has, in my opinion, a fatal
> flaw. The light source seems to be too broad to test the phenomenon.
> Furthermore it appears to be tilted at an angle at the entrance to the
> tube. Both of these factors will have the light glancing off the interior
> of the tube. At least some of the light will be at Brewster's angle for the
> interface between the sugar solution and the tube. So the interior of the
> tube becomes its own polarizer.
> Another thing that should have been mentioned is that the light, while
> circularly polarized  in the sugar solution, emerges linearly polarized.
> Maybe that's obvious, but it should have been stated.
> Having said all that, it's a hell of a beautiful demonstration. It should
> be repeated with a narrow beam of light just to see the results.
> ------- Original Message -------
> On Sunday, September 10th, 2023 at 1:15 AM, H L V <>
> wrote:
> The well known mathematics youtuber 3Blue1Brown recently published two
> interesting videos on polarized light passing through a clear glass tube
> filled with dissolved sugar in water. (He is working on a third video.)
> Normally he explains mathematical concepts with nicely rendered visual
> explanations so the inclusion of a physical demo is something new for his
> channel. The mathematical explanation offered in part 2 seems to
> qualitatively account for what is observed in part 1 but there is a lively
> discussion in the comment section on part 2 where it is pointed out that
> his explanation makes a prediction that he acknowledges is not actually
> observed. I enjoy it when textbook science bumps up against reality! It
> will be interesting to see if he can account for this theoretical weakness
> in his third video.
> This demo tests your understanding of light | Barber pole, part 1
> This demo tests your understanding of light | Barber pole, part 2
> Harry

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