Wednesday, October 6, 2010

Line Spectra Lab

Picture of white light with
continuous light spectrum.
        We did a lab called the Line Spectra Lab. In this lab we did multiple experiments that showed us and helped us to understand the 3 major different types of light spectra. Those include the: continuous spectrum, absorption spectrum, and emission line spectrum.
        The first type of spectrum we experimented with was continuous. White light, such as sunlight, will always have a continuous spectrum if it is incandescent. This means that within this spectrum the colors red, orange, yellow, green, blue, indigo, and purple will always show when the pure light is broken down. Another way to say it is, all of these colors combine to form white light and when seen with a spectroscope the colors appear in a continuous row.
        The second type of spectrum we viewed was absorption. We viewed this by putting a bottle of red colored water up against a white light. We used our spectroscopes to peer through the bottle. When I looked through my spectroscope I noticed that I saw the light being transmitted but not the light that being absorbed. From this I determined that that red light absorbs blue light because I saw a lot of red and the green/blue lights had disappeared.  In the absorption spectrum colors continue, but some may be missing.

Light Spectrum seen for the
fluorescent overhead light
        Finally, we took a look at the emission spectrum. The first thing we looked at was the overhead fluorescent light. This is a type of white light but due to the fluorescent bulb the spectrum showed up in bars of all the colors (ROYGBIV). After this we got a little more complex. We used a spectrum electric power supply to give high voltage to tubes of enclosed gasses. Each gas when lit appeared a different color to the naked eye and produced different wavelengths of colors that we saw as defined colored lines in our spectroscope. This experiment deals with electrons bouncing between energy levels of the atoms. If we would have gotten more in depth with it we could have calculated the energy of the waves based off of Plank's Constant and the frequency (E=hf). The first gas we looked at was Hydrogen. Hydrogen appeared purple to the naked eye, but when seen through the spectroscope i saw a bright red, a cyan, and a purple. One thing i noticed, which was true for all the gases we looked at, was that in between the colors we were seeing black. At first i was wondering what would cause the black, then i realized that we didn't see those colors because their wavelengths weren't visible. Their wavelengths weren't visible because they are not a possible jump for the electrons to make between the energy levels. The wavelengths that were visible, were visible because when the electron was dropping back down to the ground state it shows off the color depending on the frequency. Once i had this concept down, we looked at six different types of gases (not including hydrogen, which we had already seen) and made observations about the different colors emitted. Helium showed orange to the naked eye, but when seen through the spectroscope i saw lines of faint red, bright orange, dark green, and purple. Nitrogen appeared orange with a bit of purple at the end points of the tube, but when seen in the scope it had lines of bright red, a little yellow, green, and purple (these lines were blended a bit more than most of the other gases). Next, was Mercury. To the naked eye it appeared a light blue, but it emitted lines of very faint red, light orange, bright green, and purple. Neon came next and looks bright red to the eye, but the scope showed a lot of very bright red streaks with a orange and yellow streak as well. Dark green and dark purple were also seen, but very very faintly. Then, iodine was viewed. Iodine appeared white to the naked eye and with the specroscope I saw very bright colors red-green sort of blended together and then two very defined lines of blue and purple. Finally we looked at Argon. Argon was purple to the naked eye, but when seen through the spectroscope I was a very faint red orange, a light green, dark green, and purple line (no lines were very intense in this gas).

        All in all, these experiments that we did in this lab helped us to understand the 3 major different types of light spectra. Again, those include the: continuous spectrum, absorption spectrum, and emission line spectrum. Continuous light deals with plain white light and has a continuous streak of colors when seen with a spectroscope. The absorption spectrum has a colored light in front of white light & so when seen with a spectroscope you only see the colors that are transmitted, not absorbed. Finally, with the emission spectrum you see the break down of bars of define colors emitted, in our case, by the different gases. I learned a lot from these experiments and now truly understand the basics of each type of light spectra. For anyone else out there trying to learn the same material, I hope this helps to explain the types of light spectrums better & gives you some mental pictures to work with in order to comprehend this lab a bit easier. : )

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