Reflection of Electromagnetic Radiation in Dense Materials

[roineust]

Hello there,
Here is an elementary explanation about 'Free end reflection':

http://www.physicsclassroom.com/mmedia/waves/free.cfm

My question is:
Say we radiate from a certain direction a rigid not hollow object, that is surrounded by gas or by vacuum, with electromagnetic or other type of radiation that can pass through the object partially or more than that .
If we check the internal reflection direction of that radiation residues inside the object - will we find out that that radiation reflects inside the object at the same direction it came from or inverted?

Thanks.

 

[mfb]

I don't understand the question. Can you draw a sketch?

There will be light (or whatever) reflected back at the "exit" (back in the direction of the source), a part of that will get reflected in the opposite direction again and so on, but with a probability that goes to zero for many reflections.

 

[roineust]

Here is the sketch. No kind of radiation reflects back inside a radiated object? or hardly at all?

 

[mfb]

The lower right "?" ray will be present in general, together with the left "?" ray. The upper "?" ray is incoming light only.

 

[roineust]

Why is it that D will be present in general and not C?
Isn't it considered a 'Free end reflection' case?

 

[mfb]

You don't have a one-dimensional problem here. Incoming angle = deflection angle applies for two-dimensional problems.

 

[roineust]

Please see an updated sketch,

Do you mean that the question regarding the BEAM angle is a one dimensional question and that the answer is D angle de/reflection of the ray and not a C angle.

And that the question regarding the 'Free end reflection' is a different kind of question - a two dimensional question and has to do only with the blue or red kind of ray WAVE (phase) and that the answer to this other question, is that because of 'Free end reflection' it would be the red wave phase and not the blue wave phase which reflects?

 

[Drakkith]

By inverted, are you talking about the phase of the reflected EM wave?

 

[roineust]

Yes, the phase of the reflected EM wave.

 

[mfb]

Do you mean that the question regarding the BEAM angle is a one dimensional question and that the answer is D angle de/reflection of the ray and not a C angle.

No. The idea "the reflection is opposite to the incoming light" comes from a one-dimensional case, where there are just two directions. That idea does not work for two-dimensional cases like the one in the sketch.

 

[roineust]

I did not understand - can you please refer me to a really plain explanation of the two dimensional case vs. the one dimensional case?

 

[mfb]

Forget the one-dimensional case, that is my point all the time. Forget the "free end".

Light is reflected in the same way a pool ball bounces from a border, for example. Always the "D" path.

 

[roineust]

Forget the one-dimensional case, that is my point all the time. Forget the "free end".

Light is reflected in the same way a pool ball bounces from a border, for example. Always the "D" path.

Just to be clear about that - even if it is not a pool, in the sense that there are water surrounded by a denser material - But a pool filled with a denser material, the type that usually the edges are made of (e.g. concrete) and a less denser material (e.g. water, gas or vacuum) is what the edges are made of and the radiation travels within the denser material in the middle of the 'pool', until it reaches the less denser edge? Still only the 'D' path?

 

[theodoros.mihos]

You can think about wave equation solution for infinity wave. On different materials the wave have different wave vector k, then the continuity of k components to all axis give the reflection - refraction Snell's law.

 

[mfb]

Just to be clear about that - even if it is not a pool, in the sense that there are water surrounded by a denser material - But a pool filled with a denser material, the type that usually the edges are made of (e.g. concrete) and a less denser material (e.g. water, gas or vacuum) is what the edges are made of and the radiation travels within the denser material in the middle of the 'pool', until it reaches the less denser edge? Still only the 'D' path?

Plus B, yes. No C. And the D light will have another partial reflection at the lower edge, of course.

Light does not travel well within concrete.