Absorption/Reflection

[infrasound]

Hello,

 

First, just so you understand my level of physics knowledge, I am what you might call a layperson.

 

I have a question or two about the absorption of light by materials (solid state).

 

First, it my understanding that the light absorbed by solid lattices is due to interactions allowed by the lattice. Typically there is a particular wavelenth that will come back from the lattice, and cause what we normally would say is the color of the object(a red apple, blue shirt, orange street cone, etc).

 

My concern is with the behavior of that wavelength (that is reflected) as it interacts with the object.

 

-Does the wave simply bounce off of the object, as opposed to being absorbed, like sound off of a stiff wall?

-Does the wavelength get absorbed then emitted back out (if so, is there an analogy or picture for this)?

-Is it something else?

 

On a side note:

 

I asked some questions regarding this on another board(which I will not name). Some of the members tried to be helpful, and give me understandable analogies and such, at least to get me to the point that I am at. Other members were less than helpful. I thought I would maybe try here instead. Thanks in advance.

[swansont]

It's sort of both — you can model this as bouncing off (classical) or by absorption and re-emission (quantum mechanical). It's often easier to see and understand certain behaviors depending on which model you apply. You can apply Maxwell's equation and the boundary conditions to the problem and derive the relationships of reflection and transmission from it, and see the polarization dependence of the formula — Brewster's angle, which is the angle that has no reflection for the polarization with a component normal to the surface.

 

The classical description will not easily cover QM effects, though, so it e.g. doesn't tell you about color. But Brewster's angle is explained with the QM description as well, because an atom radiates like a dipole, and dipoles do not radiate along their axis. Which means there is some angle at which the atoms in a lattice will not radiate at that polarization.

[Klaynos]

Also, (assuming the classical description here) similarly to sound waves even if the light is reflected off there will be some small decay into the material itself.