why does the speed of light decrease in dense mediums?

Answer 1

The reflectivity of the medium obstructs the full passage of the light, thus slowing it down.

Answer 2

The speed of light decreases in ALL media. Dense media slow light down more though.

As light passes through a medium the electrons in the orbitals of the atoms absorb the photons, get excited, emit the photon (usually but not always of the same energy) and decay back into their normal state. The denser the medium, the more electrons you've packed into the space, so the more likely the absorbtion is to occur. This absorbtion takes time and, consequently, the more of these absorbitive occurances you have, the slower the effective speed of light becomes.

The speed of sound is totally unrelated to the speed of light (unless you believe in the luminous ether, which is total boswellox and was proven to be boswellox about two centuries ago). The speed of sound increases in dense media because sound is nothing more than pressure waves. In a denser medium, these pressure waves can travel faster because the medium in which the pressure 'is' is closer together.

Anyway, the speed of light is mainly effected by the effective permittivity (and permeability) of a medium. This is loosely related to density but is effected much more by the structure of the medium. A metal, for example, has a negative permittivity and a positive permeability. This means that the wave function becomes imaginary and attenuates as it passes through the metal (in other words, the light is absorbed by the metal). Ignoring reflection (as this is a surface effect), it means light can't pass through metal if the metal is thick enough. Glass has a positive permittivity and permeability, and so light can pass through. The attenuation in glass is due to material dispersion.

A new range of media (called metamaterials) have been developed which have negative permittivity AND negative permeability. These are amazing new media because the light actually travels BACKWARDS in the media. I kid you not, the phase velocity is in the opposite direction to the group velocity. This technology lends itself to perfect zero-abberation lenses and even invisability (making use of the surface plasma polaritons).

Anyway, I hope this helps.

PS: John R is right about the frequency staying the same and the wavelength and speed decreasing. Go back to school Joseph.

Answer 3

When an electromagnetic wave (light) is propagated through matter, the electric charges of the molecules are set into vibratory state.

Since an electron cloud moves freely as compared with heavy nuclei, electric oscillations consists in the displacement of the center of gravity of the electrons relative to the center of gravity of atomic nuclei’s positive charges.

Writing down an equation for the oscillations of electrons, we can find an expression for the dipole moment of a molecule.

Thus one can find an expression for the refractive index of the medium in terms of the parameters of the molecular dipole.

It shows that the refractive index depends upon the number of molecules per unit volume.

Thus when an electro magnetic wave is propagated through a medium its speed decreases whereas its frequency remains the same. Correspondingly the wave length also decreases.

The above said equation is for forced harmonic oscillations.




Theoretical Physics by A. Kitaigorodsky.

Answer 4

It's like the speed of answers and questions on this Yahoo thing. Light, like a question, becomes impeded in a dense medium (just like an easy question takes longer to get through a thick skull).

It might help to imagine light as a postman. The postman can drive his truck freely through a parking lot (not a very dense medium). If the postman drives through a crowded restaurant (denser medium) then his speed is slowed (by the twisted limbs of his victims).

Answer 5

Interesting question. And why does the speed of sound INCREASE in dense mediums?

To me this is a paradox. Both are nothing more than disturbances in space with little more difference than their frequencies.

In "waveguide theory", electromagnetic waves are considered to travel slower than the speed of light because of directionality and reflections. Waves inside a controlled medium (such as a waveguide transmission line) bounce off of the surfaces inside and thus don't travel in a straight line. The waves themselves might be traveling at the speed of light, but the wave front is slower.

I would assume that light reacts the same way as it meets obstructions.

(Note to John R: frequency and wavelength are inversions of each other. When one changes, they both change.)

Answer 6

First, gentle velocity would not inevitably shrink in a denser medium--it has not something to do with mass density. It relies upon on the index of refraction, that's the ratio of velocity interior the medium to velocity in a vacuum. besides the shown fact that, the actual reason is that gentle waves and sound waves are fairly some issues. Sound waves are compression waves interior the medium, and are changing pressures. they are going to be suffering from the compressibility and density of the medium. besides the shown fact that, gentle waves do not work together immediately with the medium. gentle waves are created from electric and magnetic fields, and the medium residences that influence those fields desperate the gentle velocity interior the medium. particularly, those residences are permittivity (touching on electric field to cost) and permeability (determining magnetic field from changing electric field). the gentle velocity relies upon on those 2 residences basically and not density.

Answer 7

Because of refraction. The frequency stays the same but speed and wave length decrease.