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Offline zinedine_88

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chemistry question...
« on: April 09, 2008, 08:11:17 PM »
An experiment determines that a certain unknown solid-state material can absorb UV light, but not light with wavelengths in the visible or IR region. Which of the following best classifies this unknown material?


The answer is AN INSULATOR...

ok My question is why?

It doesn't make sense to me that it can absorb UV light which has higher energy than the light in the VISIBLE SPECTRUM. Shouldn't it absorb both.

In our book they talk about the valence and the conducting band but they don't mention anything about light, absorbance etc...

I know that METALS are shiny because the electrons in their valence gap easily go to the conducting band since there is no band gap and emit photons.

But I can't explain why the answer of the question above is an INSULATOR.

Metals also absorb UV...

PLease explain :)

thanks


Offline Arkcon

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Re: chemistry question...
« Reply #1 on: April 09, 2008, 09:06:51 PM »
I wouldn't use the term INSULATOR in this case, unless it's the jargon of an obscure application that I haven't heard of.  Which is possible, I don't actually know everything,(really, it's true, and no snickers from the peanut gallery, please.)  On the other hand, you haven't told us what level you're at, or what you class is about.  At any rate, I would call something like that a FILTER.  Add there are plenty of UV absorbing visible transmitting substances (heard of any?).  Such a wide range of wavelengths comprise the IR, it could be possible for some thing to transmit some of them.
« Last Edit: April 10, 2008, 09:46:31 PM by Arkcon »
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline zinedine_88

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Re: chemistry question...
« Reply #2 on: April 09, 2008, 10:25:07 PM »
INSULATOR in that question refers to a material that has a big BAND GAP ( the gap between the valence gap and the conducting band)

this is truly the right answer according to a profesor in a US academic Institution.

So it is supposed to be RIGHT

My question is why?

Offline zinedine_88

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Re: chemistry question...
« Reply #3 on: April 09, 2008, 11:21:42 PM »
i am IN ENGINEERING CHEMISTRY - inorganic

so we study all basic chemistry- from the periodic table to KINETICS

so that's what my level is...:)

Offline Borek

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Re: chemistry question...
« Reply #4 on: April 10, 2008, 03:10:16 AM »
Where do the electrons in conducting band come from?

How does length of absorbed light depend on the distance between valence and conducting band?
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