In 30 seconds
A 3Blue1Brown demonstration sends white light through polarizing filters and a tube of sugar water. The short shows colored bands and changing light at the far end, then asks why the bands are diagonal without giving the full explanation.
- 1The setupA white lamp shines through two polarizers with sugar water between them.
- 2Moving color bandsRotating the first filter makes diagonal bands appear to travel along the tube.
- 3A symmetry puzzleThe final color changes with the second filter, and the diagonal stripes raise a question about the apparently symmetric setup.
Takeaways
- White light passes through a polarizer, sugar solution and a second polarizer.
- Rotating the first filter makes colored bands appear to move along the tube.
- The second filter changes the color projected beyond the tube.
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The optical setup
A lamp and two polarizers surround a tube of sugar solution.
A demonstration tests our understanding of light. A powerful lamp sends white light through a polarizing filter and a cylinder filled with sugar water; a second linear polarizer sits at the far end.
Colored bands and questions
Rotating the filters changes what is seen, prompting a question about diagonal stripes.
When the lamp is switched on, diagonal colored bands appear along the tube. Rotating the first filter makes the bands seem to travel down it, like the stripes on a barber pole.
The light emerging through the second filter is no longer white, and rotating that filter changes the color projected on the wall. The presenter asks why the stripes are diagonal when the arrangement seems symmetric from top to bottom. The short leaves the explanation to the longer video.
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