Why Does the Speed of Light Change in Different Mediums?

Click For Summary

Discussion Overview

The discussion centers around the behavior of light as it travels through different mediums, specifically addressing why the speed of light appears to change in various materials compared to its constant speed in a vacuum. Participants explore concepts related to the speed of light, refraction, and the interaction of light with matter, with a focus on both theoretical and conceptual understanding.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants assert that the speed of light in a vacuum is always c, while it changes in different mediums due to factors like density and refractive index.
  • Others question the reasoning behind the change in speed, expressing confusion about how light behaves when entering a medium.
  • A few participants propose that light is absorbed and re-emitted in a medium, suggesting that the light that exits is not the same as the light that entered.
  • There are discussions about the relationship between speed, frequency, and wavelength, with some noting that while speed changes, wavelength remains constant.
  • One participant challenges the notion of speed being multiplied when light reaches two walls simultaneously, emphasizing that speed is measured between two objects rather than from one to multiple others at once.
  • Some participants express a need for clarification on the absorption and re-emission model of light in mediums, indicating a shift in understanding based on further reading.

Areas of Agreement / Disagreement

Participants generally agree that the speed of light is constant in a vacuum and changes in other mediums, but there is significant disagreement regarding the implications and explanations of this phenomenon. Multiple competing views remain about the nature of light's interaction with matter and the models used to describe it.

Contextual Notes

Some participants note confusion regarding the terminology and concepts related to light's behavior in mediums, indicating potential limitations in understanding the underlying physics. There are also references to the need for further reading to clarify misconceptions.

Who May Find This Useful

This discussion may be useful for individuals interested in the physics of light, particularly students or enthusiasts seeking to understand the complexities of light behavior in different mediums and the theoretical models that describe these phenomena.

quantizedzeus
Messages
24
Reaction score
0
Speed of light...

It makes no sense to me that if the speed of light is always c...then in different mediums why this speed changes...?? I may have got it in a wrong way...But can anyone help me out in detail...(thanks)
 
Science news on Phys.org


The speed of light in a vacuum is always c.
 


Does it puzzle you that the speed of sound is different in air than in water?
 


quantizedzeus said:
It makes no sense to me that if the speed of light is always c...then in different mediums why this speed changes...?? I may have got it in a wrong way...But can anyone help me out in detail...(thanks)

Please start by reading the FAQ thread in the General Physics forum.

Zz.
 


The speed of light is constant in vacuum and it changes in different mediums.
when light enters a denser medium (like from air to glass) the speed and wavelength of the
light wave decrease while the frequency stays the same.
How much light slows down depends on the new medium's refractive index, n.
 


speed of light (c = 3 x 10^8) is an constant while on vacuum
but c vary in other medium depend on its density. => n = c/v while n = refractive index.
higher refractive index means less density.
CMIIW
 


quantizedzeus said:
It makes no sense to me that if the speed of light is always c...then in different mediums why this speed changes...?? I may have got it in a wrong way...But can anyone help me out in detail...(thanks)

Seems perfectly natural to me. But don't just say the speed changes. It only gets slower in a medium.

But the fact is that light is constantly absorbed and re-emitted in a medium. The light that goes out isn't the light that came in.

When a light-particle bangs into the electron cloud in an atom in a medium, it dies and is disappeared, and an impostor steals its clothes and runs out the same direction a bit later. Everyone is fooled. Even the cops.
 


danR said:
Seems perfectly natural to me. But don't just say the speed changes. It only gets slower in a medium.

But the fact is that light is constantly absorbed and re-emitted in a medium. The light that goes out isn't the light that came in.

When a light-particle bangs into the electron cloud in an atom in a medium, it dies and is disappeared, and an impostor steals its clothes and runs out the same direction a bit later. Everyone is fooled. Even the cops.

Speed of light is slower in all mediums except VACUUM.
v=frequency x wavelength

v changes but wavelength doesn't.

as v changes this causes refraction when light enters a different medium.
 


Keyur said:
Speed of light is slower in all mediums except VACUUM.
v=frequency x wavelength

v changes but wavelength doesn't.

as v changes this causes refraction when light enters a different medium.

I wouldn't include a vacuum as a medium, though. And strictly speaking, does c remain as a constant even with a medium, between re-emissions and re-absorptions?
 
  • #10


After reading the FAQ on transmission through a medium, I have to abandon the simple adsorbtion, re-emission model, although the wording at a key point in that article is a bit confusing.
 
  • #11


danR said:
Seems perfectly natural to me. But don't just say the speed changes. It only gets slower in a medium.

But the fact is that light is constantly absorbed and re-emitted in a medium. The light that goes out isn't the light that came in.

When a light-particle bangs into the electron cloud in an atom in a medium, it dies and is disappeared, and an impostor steals its clothes and runs out the same direction a bit later. Everyone is fooled. Even the cops.

so the light particle that come in will stay there ?? or what ?
 
  • #12


If the light bulb is in the midle of the room and you turn it on the light reaches south wall same time as north wall. Does that mean you multiply the speed of light times 2?
 
  • #13


No, it doesn't. Speed is measured from one object to another. Not from one object to two others at the same time. That's not speed.
 
  • #14


piroman said:
If the light bulb is in the midle of the room and you turn it on the light reaches south wall same time as north wall. Does that mean you multiply the speed of light times 2?

You need to read up on what light is. Hit up wikipedia and the FAQ here on PF.
 

Similar threads

  • · Replies 52 ·
2
Replies
52
Views
14K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 30 ·
2
Replies
30
Views
4K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 31 ·
2
Replies
31
Views
7K
  • · Replies 19 ·
Replies
19
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K