Light Isn't Constant in Certain Media?

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SUMMARY

Light does not travel at a constant speed across different media; it travels slower in materials such as water and glass compared to its speed in a vacuum. Specifically, light travels at approximately three-fourths of its vacuum speed in water. This phenomenon occurs because light interacts with the atoms in the medium, being absorbed and reemitted, which delays its overall travel time. Understanding this behavior is crucial for grasping fundamental physics concepts related to light propagation.

PREREQUISITES
  • Understanding of basic physics principles, particularly optics.
  • Familiarity with the concept of the speed of light in a vacuum.
  • Knowledge of light-matter interactions, including absorption and reemission.
  • Basic comprehension of different media properties, such as water and glass.
NEXT STEPS
  • Research the concept of refractive index and its impact on light speed in various media.
  • Explore the principles of light absorption and emission in atomic physics.
  • Learn about the implications of light speed variations in optical technologies.
  • Investigate the historical context of Newton's theories on light and their evolution.
USEFUL FOR

Students of physics, educators in optics, and anyone interested in the fundamental properties of light and its behavior in different environments.

Liger20
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Hello, I was recently browsing through on of my physics books, and I came upon the following statement:

"Newton was right, light does travel at a constant speed, but it does not travel at the same speed in all media. For example, light travels at a speed in water that is about three fourths the speed of light in a vacuum. The speed of light in air is slightly less than the speed in a vacuum."

I found this statement disturbing, because I've always been taught that light always travels at a constant speed. It not that I don't believe that it travels slower in water than in a vacuum, but my question is why does light behave like this?

Also, what is the medium through which light travels, if any?
 
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Liger20 said:
but my question is why does light behave like this?
In vacuum light just travel and its speed is maximum possible.

In water, glass or air light not only travels, but also being absorbed and reemitted by media atoms. This process takes some time. So, it has less time to travel. The result is slower traveling in media other than vacuum.
 
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