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Author Topic: How does foil reflect infrared (IR) radiation?  (Read 12094 times)

Matthew Burnett

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How does foil reflect infrared (IR) radiation?
« on: 02/08/2009 23:30:03 »
Matthew Burnett asked the Naked Scientists:
   
Could you please explain why metals such as aluminium foil reflect infra red radiation in terms of their properties and atomic structure?

What do you think?


 

lyner

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How does foil reflect infrared (IR) radiation?
« Reply #1 on: 03/08/2009 07:12:44 »
Hi
Reflection by metals is caused by the fact that the outer electrons are very loosely bound to any particular atom. They are, effectively, shared by all the surrounding atoms. This accounts for the high electrical and thermal conductivity of metals (and also their strength even when stretched and deformed).

When any electromagnetic wave arrives at a metal surface, the conduction electrons are vibrated by the varying fields and re radiate the energy as a reflected wave. For a flar surface, a mirror (coherent) reflection is produced. This works for light, I.r. And all radio waves.
X rays have such high photon energy that they tend to penetrate except at 'grazing' angles.
« Last Edit: 03/08/2009 07:15:12 by sophiecentaur »
 

Offline Matthew

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How does foil reflect infrared (IR) radiation?
« Reply #2 on: 05/08/2009 16:30:44 »
Thank you!
You said the outer conducting electrons are vibrated by the varying fields. What are the "varying fields"?
I can understand they re-radiate the electromagnetic energy as a reflected wave but why? Why don't these electromagnetic waves just get absorbed by the outer electron? Does the degree of reflection or transmittance of an electromagnetic wave depend on its photon energy too?
 

lyner

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How does foil reflect infrared (IR) radiation?
« Reply #3 on: 06/08/2009 20:03:08 »
The electrons are caused to flow by  the varying em fields of the wave. A radio receiving antenna works for that reason. The receiver absorbs some of the energy of the moving electrons (current). A transmitting antenna radiates because the transmitter drives the electrons into oscillation. A length of wire will act as both receiving and transmitting antenna - a reflector.
It works best as a reflector if it is the right length but, for metal objects of many wavelengths in size, the reflection works, by the same principle but over a large area. There is very little loss because metals do not absorb the energy of the oscillating electrons (or at DC).
 

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How does foil reflect infrared (IR) radiation?
« Reply #3 on: 06/08/2009 20:03:08 »

 

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