Light Speed Increase: Reasons & Explanations

[Olly]

IM not sure that this question should be here or in some other forum, anyway here is my question :

When light travels from a more dense material to a less dense one (say from water to air) the light speeds up again. However i would like to know WHY it speeds up again, and what gives it the energy to do so, as it doesent seem to accelerate (or I've never heard that it does)

 

[Hydr0matic]

https://www.physicsforums.com/showthread.php?s=&threadid=1069

 

[R0man]

The increase in light speed when traveling from a more dense material to a less dense one is due to the change in the medium's refractive index. Refractive index is a measure of how much a material can slow down or bend light as it passes through it. When light enters a more dense material, the refractive index is higher, which means the speed of light is slower. As it exits into a less dense material, the refractive index decreases, allowing the light to travel faster.

This change in refractive index is due to the interaction between light and the atoms or molecules in the material. When light enters a material, it interacts with the atoms or molecules, causing them to vibrate and absorb some of the light's energy. This absorption slows down the light. When the light exits into a less dense material, there are fewer atoms or molecules to interact with, so the light can travel faster.

It is important to note that light does not actually accelerate in this process. The speed of light is a constant in a vacuum, and it is only the interaction with the material that affects its speed. Additionally, the energy for this change in speed comes from the light itself, as it is constantly being absorbed and re-emitted by the atoms or molecules in the material.

In summary, the increase in light speed when traveling from a more dense material to a less dense one is due to the change in refractive index and the interaction between light and the atoms or molecules in the material. This change in speed does not involve acceleration, and the energy for it comes from the light itself.