# Wave passing medium containing discontinuities?

1. Jan 17, 2010

### timlee

When a wave is passing medium containing discontinuities, I learned from Wiki, scattering means changing the direction from a straight trajectory, so does it include refraction, transmission and reflection?

Does transmission means the part of wave that has passed the interface, and therefore include refraction and scattering, not reflection? Or transmission mean the part of wave still in the straight trajectory?

What would possibly happen when a wave hits the interface of discontinuities? Reflection, refraction, absorption? anything else not mentioned?

In the cases of Reflection, refraction, scattering and transmission, will the atom hit by the light absort the light and/or remit a new light?

Thanks!

Last edited: Jan 17, 2010
2. Jan 17, 2010

### Noxide

I'm kind of interested too.

I imagined two scenarios, a water wave in a finite glass bowl. We all know what happens there, and the other scenario is a wave travelling through air and then hitting a a vacuum border. I'm not quite sure what will happen in the second, but I think it may be similar to the first, or it may just eliminate the wave completely.

3. Jan 17, 2010

### Bob S

When light passes from medium 1 with index of refraction n1 to medium 2 with index n2, the fraction of power reflected (= not transmitted) at the boundary is

Fraction of power reflected = (n2-n1)2/(n2+n1)2

For example, light entering glass (n=1.5) from air (n=1) loses fraction 0.04 of power per interface, 0.08 per single pane window. This does not include any interference of reflected waves.

Bob S

4. Jan 17, 2010

### timlee

Thanks! In my original post, I actually wanted to ask the difference of those concepts, especially scattering and transmission with other concepts. So if anyone can help me to clarify these concepts, I would really appreciate it.

5. Jan 18, 2010

### Claude Bile

No, scattering does not include refracted (transmitted) or reflected waves.

In this scenario, the waves are generally broken up into 3 components. The incident wave, transmitted (or refracted wave) and the reflected wave.

It depends on the boundary conditions. If you mean EM waves, then you get reflected and transmitted waves (except in very specific cases). Scattering too can originate from boundaries. Absorption however is usually regarded as happening within a volume and not at a boundary.

With regard to transmission and reflection, atoms do not absorb and re-emit EM waves in the sense that the electron is promoted to a new orbital and then relaxes back into the ground state. Refraction etc. is actually a result of atoms polarising in response to the applied EM field, without the wave being absorbed.

The question of whether you get the "same" wave is irrelevant in the sense that you can successfully describe nature using either the single-wave or many-wave viewpoint.

Claude.

Last edited: Jan 18, 2010
6. Jan 19, 2010

### timlee

Thanks, Claude.
Does transmission include scattering and refraction?

7. Jan 19, 2010

### Bob S

A good example of classical light scattering is Rayleigh scattering of sunlight. Individual molecules of air preferentially absorb blue light of a particular incident light polarization, and re-emit it in a classic electric dipole radiation pattern. See
http://en.wikipedia.org/wiki/Rayleigh_scattering
This is why blue skylight (from a clear-blue sky) viewed at 90 degrees to the Sun is almost completely polarized.
Bob S