Speed of Light: Get Answers to Your Questions

Click For Summary

Discussion Overview

The discussion revolves around the behavior of light as it travels through different media, specifically addressing the change in speed when light passes through glass and then returns to its original speed in air. Participants explore the implications of this change in speed and the energy considerations involved.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions where light gets the energy to speed up again after exiting glass, suggesting a need for clarification on energy dynamics.
  • Another participant asserts that light does not require energy to speed up because it has no mass and therefore no kinetic energy, emphasizing that the energy of a light ray is determined by its frequency, not its speed.
  • A different participant notes that the speed of light in a medium is an observed speed and that individual photons always travel at the same speed, suggesting that the change in speed is only apparent and not actual.
  • This participant further claims that once light exits the medium, it returns to its original speed without gaining energy, implying that the speed change may not be a true alteration.

Areas of Agreement / Disagreement

Participants express differing views on the nature of light's speed change in media and the associated energy considerations. There is no consensus on whether the speed change is real or merely apparent, and the discussion remains unresolved.

Contextual Notes

Some statements rely on specific interpretations of energy and speed in relation to light, which may depend on definitions and assumptions about light's behavior in different media.

naab
Messages
16
Reaction score
0
Hey

If you shoot a beam of light through a piece of glass, the speed of the light changes..

When the beam exits the glass again it speeds up to the speed light has in air, right?

So my question is, where does the light get the energy to speed up again from?
 
Science news on Phys.org
It doesn't need energy to speed up because it doesn't gain kinetic energy in speeding up (light has 0 mass and so 0 kinetic energy). The energy in a light ray depends on its frequency, not speed.
 
ahh okay.. thanks
 
You can also look here:
https://www.physicsforums.com/showpost.php?p=899393&postcount=4
 
Last edited by a moderator:
naab said:
Hey

If you shoot a beam of light through a piece of glass, the speed of the light changes..

Also note that the speed of light referred to is the observed or measured speed in some medium and not the true speed of light (as observed in vacuum). Individual photons always travel at the same speed. The change is only apparent.

Once the light has emerged from the medium it changes back to its original speed and this is without gaining any energy. This can mean only one thing—that the light's speed itself was never altered in the first place.
 

Similar threads

  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 25 ·
Replies
25
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 24 ·
Replies
24
Views
3K
  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 207 ·
7
Replies
207
Views
14K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 8 ·
Replies
8
Views
9K
  • · Replies 9 ·
Replies
9
Views
3K