Does speed of light changes?????

[udhitsharma]

i just wnna know that if we change the medium does the speed of the light changes?

if yes then how it is affected. is there any forumla or any other mathematical relation which explains about this?????:)

[Tormod]

You're probably looking for the refractive index.

[arkain101]

Complicated question.

 

The speed of light, the constant of light, and the velocity of light are varyiable in how you are refering to them.

 

From point A to B the velocity of light can change. Be it the material or lack of material it passes through or the changing velocity of the source of the light you are detecting like a star orbiting an object in space, changing its ditance and velocity relative to you.

 

It is quite well summed up here in the first section:

 

http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/speed_of_light.html

[kamil]

Another interesting point similair to the one bieng made is how this change in the speed of light affects Special Relativity.

Because imagine setting up that gedanken for showing time dilation. But this time, it occurs in a place where the medium will make the speed of light lower than 'c'. Obvioulsy the lorentz factor will change, meaning that the time dilation yielded from the time dialation formula will be different.:shrug: :hihi:

[Jay-qu]

Another interesting point similair to the one bieng made is how this change in the speed of light affects Special Relativity.

Because imagine setting up that gedanken for showing time dilation. But this time, it occurs in a place where the medium will make the speed of light lower than 'c'. Obvioulsy the lorentz factor will change, meaning that the time dilation yielded from the time dialation formula will be different.:shrug: :hihi:

 

no, not quite, the speed of light is nothing special in any medium, its when it is without medium, at c, that it has meaning.

[kamil]

no, not quite, the speed of light is nothing special in any medium, its when it is without medium, at c, that it has meaning.

 

So is the speed of light NOT the same for all observers when there is a medium? Is that why all the concequences of Relativity remain true? :lol:

[Jay-qu]

Im not to sure what you mean.. but light still propergates at c no matter what the medium, its just in more optically dense materials the light is slowed down because of interactions with matter. This has no effect on relativity.

[kamil]

Im not to sure what you mean.. but light still propergates at c no matter what the medium, its just in more optically dense materials the light is slowed down because of interactions with matter. This has no effect on relativity.

 

Isn't that contradictory:confused:

 

Or maybe i misunderstood you. Is there a difference between 'medium' and 'optically dense material'

[Qfwfq]

An important thing to realize is what I added to my sig, because I so often find the need to point it out.

 

It is called "the speed of light" for historical reasons but whar SR really shows is that c is a property of space-time. The dynamics condemn any massless body to have this speed, this meaning that the body has kinetic energy but no rest energy.

 

In a medium (which really just means there are a lot of atoms around) the complex interaction of the photon with these is the reason for the slowdown. This however is not the same as saying that c is decreased. For one thing a particle, such as an electron, entering the medium at high velocity can be travelling faster than light in that medium and this results in Cherenkov radiation.

[kamil]

Also, Can u tell me if u understand Special Relativity. So that I can ask you specific questions.

[kamil]

O ok, thx a lot guys, now i understand:)

[HydrogenBond]

When light passes through a refracting medium, the speed of light remains the same. What is happening is the light is taking time to smell the roses, so to speak. But between roses it is going at C. The extra distance it travels in refracting mediums is a reflection of how long it smells the roses. Diamonds appear to smell better to light than water as reflected by its higher refractive index.

[Qfwfq]

This is a cute analogy of the well-known interpretation of field theory. :)

 

It should be however said that it shouldn't be taken too literally, it doesn't make too much sense to distinguish between the photon "going the roses" when the distances betwen them is small compared with the wavelength. As usual, quantum descriptions can't be so blithely translated into classical intuitive notions. The interactions between photon and atoms are usually soft (when they aren't, it's a scattering event and that's a different kettle of fish) and all the absorbtions and re-emissions are only "kinda meta-happening", it's a semi-classical description of something that isn't classical at all.

 

If the lense can focus most of the light according to wave optics, then the potons aren't really quite getting absorbed and re-emitted by single atoms.