Interference of light, emission spectroscopy prac. report

In summary, the conversation was about a practical report due the next day involving taking angular measurements for the emission lines of Mercury spectrum using a spectrometer and Mercury spectral tube. The results were calculated using the diffraction grating formula and some assumptions were made for lines appearing in multiple orders. The conversation then moved on to discussing potential errors, including the use of a common factor for all measurements, the accuracy of angles in different orders of spectrum, and the impact of a phosphor coating on the spectral tube. The poster also requested any additional errors that may have been overlooked.
  • #1
cumlord
Ok, so I've got a practical report due tomorrow and I just wanted to clarify a few things. A bit of background knowledge first. The practical involved taking angular measurements for the emission lines of the Mercury spectrum using the apparatus, a spectrometer and a Mercury spectral tube, pictured here: http://imgur.com/Xkp8J01

We were supposed to use these recorded angular measurements to calculate the wavelengths of light corresponding to these emission lines using the diffraction grating formula dsin(theta)=m(lambda) where m is the order of the spectrum, and d is the distance between the slits (which was 1693nm). The results we collected, and the subsequently calculated wavelength values, are pictured here for the lines to the right of the central maximum: http://imgur.com/1ituoqq

and here for those to the left of the central maximum (Red-1 was treated as the maxima used throughout calculations since it was of the strongest intensity. The rest are assumed to be ghost lines): http://imgur.com/Xw0RzEa

As you can see, the angular measurements differ on either side of the central maximum, and so, where applicable, I added the angle recorded for a maximum within a certain order spectrum on one side of the central maximum to the angle recorded for the other side for the same emission line, and divided the result by two (Here's an image that shows my workings: http://imgur.com/hr5cBDo). For the emission lines that appeared in numerous orders, the results from the above process were averaged (Again, my working for this: http://imgur.com/eoKOlGD).

My questions are as follows:

1.) Why is the angle measured for a certain emission line in the first order spectrum seen as more accurate than the angle measured for the same emission line in the second or third order spectrum? Is it because of the faintness of the emission lines in greater order spectra, or is it because they involve greater angular measurements which leaves a greater margin of error?

2.) The theoretical Mercury spectrum that I am using is pictured here: http://imgur.com/Czr6wmD As you can probably tell, the wavelength values for the orange and aqua emission lines differ significantly from the values we obtained. Is it perhaps because the spectral tube we used contained a different isotope of Mercury or perhaps some impurities? I've read that Mercury lamps usually have Phosphor coatings on the outer bulb. Could some of the unexplained observed emission lines be due this Phosphor?

3.) Can you suggest any errors that may apply to this practical? I've thought of 2 systematic and 2 random but I feel I need more.

I understand a lot of people are busy so any help would be much appreciated. If you require any other information to answer the questions please ask. Also, if you spot any errors in my results, calculations, or anywhere else please let me know.

Thanks in advance.
 
Physics news on Phys.org
  • #2
Hello cum, :welcome:

Bit of a hurry eh ?
I think you did some pretty good measuring work: my compliments. Working it out the way you do is reasonable, but there is some room for improvement. In particular: the 1693 nm is a common factor for all observations, hence a systematic error source -- it does not average out. As I expect you already thought (what are your 2 systematic and your 2 random errors ?).

To answer your questions:
1. Says who ? I can imagine the small angle approximation ##d \tan\theta = m\lambda ## (with ##\tan\theta = y/L## where y is a perpendicular distance on a screen that is L away) introduces a small error for higher orders, but your instrument measures actual angles.

2. The phosphor on mercury lamps for lighting smears out the spectrum for a fraction of the light. Your lines are actual mecrury lines.

3. PF culture is to help find answers, not to rob posters from their exercise :smile: So: you list your error sources and I'll try to comment. However, I don't expect I can improve on what you have already, ...
 
Last edited:

Related to Interference of light, emission spectroscopy prac. report

1. What is the purpose of an interference of light emission spectroscopy prac. report?

The purpose of an interference of light emission spectroscopy prac. report is to document and analyze the results of an experiment that measures the interference patterns of light emitted by a sample. This allows for the identification and quantification of elements present in the sample.

2. How is interference of light used in emission spectroscopy?

In emission spectroscopy, light is used to excite the atoms or molecules in a sample, causing them to emit light of specific wavelengths. This emitted light is then passed through a prism or diffraction grating, which separates it into a spectrum of different wavelengths. By measuring the interference patterns of this spectrum, the elements present in the sample can be identified and their concentrations can be determined.

3. What factors can affect the results of an interference of light emission spectroscopy experiment?

The results of an interference of light emission spectroscopy experiment can be affected by factors such as the quality and stability of the light source, the composition and purity of the sample, and the accuracy of the measuring equipment used. Other factors, such as temperature and pressure, may also play a role in the emission of light from the sample.

4. What are the advantages of using interference of light in emission spectroscopy?

One of the main advantages of using interference of light in emission spectroscopy is its high sensitivity, allowing for the detection and quantification of trace amounts of elements in a sample. It also provides a non-destructive method of analysis, as the sample is not altered during the experiment. Additionally, interference of light emission spectroscopy can be used to analyze a wide range of elements, from metals to non-metals.

5. How are the results of an interference of light emission spectroscopy experiment interpreted and reported?

The results of an interference of light emission spectroscopy experiment are typically interpreted and reported by analyzing the interference patterns of the emitted light spectrum. This involves comparing the observed patterns to known standards or reference spectra to identify the elements present in the sample. The results are then presented in a report, which may include a discussion of the experimental procedure, the data collected, and the conclusions drawn from the analysis.

Similar threads

  • Introductory Physics Homework Help
Replies
4
Views
3K
  • Introductory Physics Homework Help
Replies
1
Views
778
  • Introductory Physics Homework Help
Replies
13
Views
4K
  • Introductory Physics Homework Help
Replies
12
Views
2K
  • Introductory Physics Homework Help
Replies
5
Views
1K
  • Introductory Physics Homework Help
Replies
2
Views
2K
  • Introductory Physics Homework Help
Replies
4
Views
2K
Replies
2
Views
3K
  • Introductory Physics Homework Help
Replies
5
Views
2K
  • Introductory Physics Homework Help
Replies
2
Views
1K
Back
Top