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Why does light slow down in water?

Fermilab · 1.3M views · 2019-02-20 · 10:24

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Overview

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.

On Hacker News

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

Recommended by 3 HN people across 3 months · HN mentions 2020–2023

Topics

Fundamental physicsEveryday physics & science demos
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speed of lightopticsphysics misconceptionswave mechanicsrefraction

What people said

gcanyon · 2023-12 · Recommendation

For anyone who's interested, Fermilab has done several videos on this topic as well that I found highly informative: [VIDEO] [LINK]

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djmips · 2023-01 · Recommendation

I had thought because light was absorbed and re-emitted but that and scattering ideas are incorrect. See this video for an explanation of why light travels slower through a medium with an index of refraction greater than one. [VIDEO]

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gugagore · 2020-12 · Recommendation

For a video to address this misconception of the speed of light being constant, and it just appears to slow down due to ping-pong, I recommend "Why does light slow down in water?" by Fermilab: [VIDEO]

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Sources

Video by Fermilab, played through YouTube.

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