Date: Wed Oct 29 14:32:36 2008

Author: Adam Beehler

Subject: Re: absorption spectra

Post:

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I have done three different versions:

(1) The aforementioned diffraction grating on an overhead projector,
slit of white light coming from the platform, and various "filters" in
between. (Yes, Doug, one of those pinkish-orangish glow-doodler plastic
sheets works well.) This is by far the most popular in the way of what
instructors ask for.

(2) The aforementioned salt on a Bunsen burner to produce a yellow
(sodium) flame. Shining white light through the flame and onto a screen
produces no shadow, but shining light from a sodium lamp through the
flame and onto a screen produces a shadow. The sodium light is absorbed
by the sodium burning in the flame. I actually prefer to use a
"white-looking" blacklight (I think they are called "blue" blacklights),
instead of white light. I shield most of the light from the screen as
well. In this way, the stuff on the screen is more discernible.

(3) I heard about these light bulbs that produce their own absorption
spectra (similar to the high-pressure sodium lamps). They are GE Reveal
bulbs. The GE Reveal bulb is marketed as the bulb that is made to
"specially filter out yellow rays that hide life's true colors." This
is accomplished by the use of neodymium in the glass. Upon heating, Nd
reacts vigorously with oxygen to form neodymium oxide (Nd_2 O_3 ), a
light blue powder. If you examine the GE Reveal bulb in comparison with
a GE "soft white" bulb, you'll notice that it has a bluish tint. The
spectrum of the GE Reveal bulb exhibits two broad absorption lines in
the yellow region of the spectrum. These correspond to a fairly broad
absorption band, from about 560 to 590 nm, in the yellow region of the
spectrum because of the neodymium oxide in the glass. I have since
found that some other "neodymium" bulbs works, too. I even found a GE
Reveal neodymium clear line filament tube-like bulb, which is better for
viewing directly with a diffraction grating.

*http://tinyurl.com/b2yx8
**http://tinyurl.com/2e94oj*
*http://aer.noao.edu/cgi-bin/article.pl?id=260

*I prefer how (2) and (3) work because they are more like an actual gas
cloud absorbing passing light, but of course, (3) is so much easier to
set up, and cheaper.

Adam Beehler




Anthony Lapinski wrote:
> In my high school astronomy class, I will be discussing light and spectra
> soon. I wish to do a lab/activity where students can analyze various light
> sources with a diffraction grating. It is easy to show continuous spectra
> with a candle or light bulb, and emission spectra with gas tubes. I am
> looking for a way to show an absorption spectrum. In the past I had
> students use colored filters to cover an incandescent light bulb. This
> sort of mimics the atmosphere of a star.
>
> Does anyone have other ways to show absorption spectra using simple
> materials?
>


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I have done three different versions:

(1) The aforementioned diffraction grating on an overhead projector,
slit of white light coming from the platform, and various "filters" in
between. (Yes, Doug, one of those pinkish-orangish glow-doodler
plastic sheets works well.) This is by far the most popular in the way
of what instructors ask for.

(2) The aforementioned salt on a Bunsen burner to produce a yellow
(sodium) flame. Shining white light through the flame and onto a
screen produces no shadow, but shining light from a sodium lamp through
the flame and onto a screen produces a shadow. The sodium light is
absorbed by the sodium burning in the flame. I actually prefer to use
a "white-looking" blacklight (I think they are called "blue"
blacklights), instead of white light. I shield most of the light from
the screen as well. In this way, the stuff on the screen is more
discernible.

(3) I heard about these light bulbs that produce their own absorption
spectra (similar to the high-pressure sodium lamps). They are GE
Reveal bulbs. The GE Reveal bulb is marketed as the bulb that is made
to "specially filter out yellow rays that hide life's true colors."
This is accomplished by the use of neodymium in the glass. Upon
heating, Nd reacts vigorously with oxygen to form neodymium oxide (Nd2O3), a light blue powder. If you examine the GE
Reveal bulb in comparison with a GE "soft white" bulb, you'll notice
that it has a bluish tint. The spectrum of the GE Reveal bulb exhibits
two broad absorption lines in the yellow region of the spectrum. These
correspond to a fairly broad absorption band, from about 560 to 590 nm,
in the yellow region of the spectrum because of the neodymium oxide in
the glass. I have since found that some other "neodymium" bulbs works,
too. I even found a GE Reveal neodymium clear line filament tube-like
bulb, which is better for viewing directly with a diffraction grating.

http://tinyurl.com/b2yx8
http://tinyurl.com/2e94oj
http://aer.noao.edu/cgi-bin/article.pl?id=260

I prefer how (2) and (3) work because they are more like an actual
gas cloud absorbing passing light, but of course, (3) is so much easier
to set up, and cheaper.

Adam Beehler




Anthony Lapinski wrote:

In my high school astronomy class, I will be discussing light and spectra
soon. I wish to do a lab/activity where students can analyze various light
sources with a diffraction grating. It is easy to show continuous spectra
with a candle or light bulb, and emission spectra with gas tubes. I am
looking for a way to show an absorption spectrum. In the past I had
students use colored filters to cover an incandescent light bulb. This
sort of mimics the atmosphere of a star.

Does anyone have other ways to show absorption spectra using simple
materials?






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