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Why does light slow down in water?

Fermilab · explainer · Watch on YouTube

Fundamental physicsEveryday physics & science demos

What it is

Fermilab's Don Lincoln explains why light travels slower in water and glass. He knocks down common wrong explanations such as absorption and re-emission, then gives the wave-mechanics reason tied to refractive index.

Why Hacker News recommends it

HN commenters link it to correct the widespread misconception about why light slows in a medium.

  • 3 people recommended it
  • 3 different months
  • 0 strong recommendations
  • first 2020, last 2023

What HN commenters said

  1. “For a video to address this misconception of the speed of light being constant”

    Corrects the misconception about light slowing in media.

    gugagore, 2020-12 · Recommendation · in “Well, Actually – Physics Answers”

  2. “See this video for an explanation of why light travels slower through a medium with an index of refraction greater than one.”

    Why light is slower in media with higher refractive index.

    djmips, 2023-01 · Recommendation · in “Ask HN: Concepts that clicked only years after you first encountered them?”

  3. “Fermilab has done several videos on this topic as well that I found highly informative”

    Fermilab videos on refractive index.

    gcanyon, 2023-12 · Recommendation · in “What is a zero refractive index material?”

Excerpts from Hacker News comments, linked to the originals. Summaries and labels were written by a language model from those comments.

Topics: speed of light, optics, physics misconceptions, wave mechanics, refraction

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