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Spectroscopy by simple means
Panteleimon Bazanos
Secondary education teacher Chemist
Abstract. Spectroscopy is a field of science that has not been given much attention in the preparation of curricula inGreece, despite its importance to the understanding of our word. In the present paper we investigated some areas ofcurricula that spectroscopy can be integrated using some activities combining experimental constructions made ofsimple and useless materials and everyday technology such as PCs, cameras and free software, through a STEMperspective.
Keywords: Spectroscopy, optical disks, constructions, STEM activities
1. Introduction
Spectroscopy and spectroscopic analysis is a field of science that has offered and still offers muchto our understanding of the world and in our culture. Its range applies from the smallest (atoms) tothe largest (galaxies) bodies. But our educational system seems to ignore this field, perhaps becauseit considers it is a difficult subject, students will hardly understand the issues dealt with or maybethe instruments required are expensive. In the curricula of the three school levels (primary, middlehigh school, hight school) there are cognitive areas related to spectroscopy (colors, rainbow, skycolor, emission and absorption spectra, atomic structure) and the negotiation of these issues whileusing a spectroscope can activate the “observation – hypothesis – experiment – verification orrefutation – feedback” scheme and make learning more interesting and effective.
In this paper, we will show using some examples, that spectroscopy can be incorporated in thelearning process of all school ages using optical disks to handmake spectroscopes and performactivities with them, that include many disciplines (science, technology, mathematics, design,photography).
2. Optical disks as spectroscopes
Because of their design, optical disks (CDs, DVDs) contain a diffraction grating which can create“rainbow” colors when illuminated by a wide spectrum light source.
Picture 1. Daylight spectrum on the surface of a DVD
Diffraction gratings are widely used in manufacturing optical spectroscopes, so we can use
diffraction gratings from CDs and DVDs to made improvised spectroscopes [1]. These handmadespectroscopes can be simple as eyeglass spectroscopes or more complicated as devices that can beadapted to cameras, camcorders or mobiles for spectrum monitoring and processing [2].
Picture 2. Eyeglass spectroscopes
Picture 3. A spectroscope that can be adapted on a camera
Starting with a piece of CD or DVD and having as final goal the construction of experimentaldevices, students will engage in a process to plan and organize their learning, to raise questions andgive answers, discuss and plans collectively, to do research on a variety of sources, analyze andpresent data, to develop a thinking framework, to present and explain their plans and solutionsproposed, to record and evaluate the progress of their learning.
3. Compatibility with the curricula
At all levels of education there are science areas where handmade spectroscopes based on opticaldisks can be used.
3.1. Kindergarten – first classes of Primary School
In this level, simple activities involving observations of luminous bodies through optical disks areproposed. The colors on the CD’s surface can stimulate little pupils, so they can easily madeeyeglasses as those in picture 2 and then they can observe the daylight entering the class or the light
emitted from the class bulbs or from other sources. Also, field observations, such as observation ofthe moon, a lightened store in the city at night, the sunset, etc, can be done.
Picture 4. Little pupil looks luminous bodies through eyeglasses made of CD.
Picture 5. Looking through a CD a lightened store at night.
3.2. Last classes of Primary School – Junior High School – High School
The running curricula of these educational levels contain topics (bodies color, light and lightseparation, atomic structure) where experimental constructions based on optical disks can be used.In this category, experiments and activities related to the spectra of luminous bodies (classificationactivities) and the identification of substances according to their light spectrum (chemical analysis)are proposed. For example, students can made their own spectroscopes and then observe the lightemitted from various luminous bodies, such as light lamps of different types, the light of a candle,etc, and try to find similarities and differences. Yet, by observing the spectrum of light that objectsemit, students can approach the subject of color perception. Finally, knowing the spectra of somereference substances, students can find out the composition of other substances (eg. If we know thespectra of magenta, cyan and yellow inks, we can find out what inks was used to paint a gelatinpaper green). Also, interdisciplinary projects about light can be designed, that rely on use of opticaldisks as spectroscopes.
Two simple examples of these ideas are given next.In the images below, some spectra have been taken having putting a piece of CD ahead of thecamera’s lens: Daylight (a), full moon (b), cfl lamp (c), gas flame (d), candle flame (e).
Picture 6. Photos of spectra having putting a piece of CD ahead of camera’s lens
Picture 7. The previous spectra after some processing
The images in picture 7 have been derived from those of picture 6 using an image processingsoftware by copying a strip of 23 pixels width from the central area of each image and then pastingthem several times.
In the picture below (picture 8), photos of white light spectra that has passed through oils areshown: virgin olive oil (a), pomace oil (b), sun flower oil (c) and a mixture of 50% virgin olive oil –sunflower oil (d). The spectra have been taken using a piece of CD ahead of the camera’s lens.
Picture 8. Spectra of white light that has passed through oils
a b c d e
a b c d e
Using the spectroscope of picture 3, one can obtain spectra that have many details. Such spectra areshown in the following pictures.
Picture 9. Daylight spectrum
Picture 10. CFL lamp light spectrum
Picture 11. LED lamp light spectrum that has passed through a potassium permanganate solution
3.3 Application in Chemistry – A STEM approach
Solutions cover a large portion of school Chemistry and spectroscopes play a major role indetermining the concentration of them. This situation is quite convenient to attempt a approachwithin a STEM perspective that could be generally described by the following steps:
1. Stimulation of students interest about light and the information it can give us involvingscience, technology and mathematics (vision, colors, microscopes, telescopes, star light,equations about light, spectra, spectroscopes, etc)
2. Construction of simple handmade spectroscopes and taking spectra with them (daylight,light of various types lamps, light that has passed through colored solutions, etc)
3. Evaluation of the obtained spectra with respect to the information they provide.4. Particular evaluation for the possibility of exploiting of the spectra obtained in chemical
analysis (spectra of colored solutions, Beer – Lambert law).5. Conception of a procedure for determining the concentration of a substance in a solution.6. Implementation of the process (eg. selection and/or construction of the parts,
interconnection of the parts, mathematization where needed, execution, valuation,presentation).
A procedure like the above, can boost students to identify questions, to seek solutions, to doresearch, to collect and organize data, to think mathematically, to design experimental apparatus, sostudents can helped to consider the interconnections between science, technology and mathematicsand by strengthening engineering disciplines they be able to act creatively and innovatively in thelife.
All of the above could result in a specific implementation, in which the spectroscope of picture 3by exploiting the visible spectrum of light and in combination with a camera, a computer andappropriate software, leads to the calculation of concentration of a colored solution as following:
1. Capturing the spectrum of light that passes through the solution2. Importing the image in the computer.3. Using an image editing software (Gimp for example) to desaturate the image and save it as
FIT file [3].4. Introducing the FIT file into the FV software (NASA’s HEASARC software) and producing
the spectral profile [4], [5].
Picture 12. Schematic representation of taking the spectral profile of a solution with FV
Having available to us the spectral profile, we can calculate the absorption of the solution using theBeer – Lambert law and assuming that the power of radiation comes out of solution is proportionalof the “counts” that FV software calculates.
Picture 13. The implementation of Beer – Lambert law in our case
A ≃ logPblank
Psample
= loga⋅Countsblank
a⋅Countssample
= logCountsblank
Counts sample
= ε⋅b⋅c = k⋅c
Schematically and in summary, the process of concentration calculation is shown in the picture below [6].
Picture 14. Making calibration curve to calculate the concentration
4. A chance
Modern mobiles (smartphones) can run computer applications and there are many of them aboutlight that take input from an external device or a photo. Thus, all procedures schematicallydescribed in pictures 12, 13, and 14 is possible to be integrated in a modern mobile, so, this devicecan function as a spectrophotometer.
Picture 15. Handmade spectroscope mounted on a mobile
5. In conclusion
Because the light plays an important role in our life and because the light – matter interaction leavesmarks that reveal much about our world, dealing with spectroscopy is a worth in the whole range ofschool ages. The construction of simple spectroscopes from optical disks is simple and inexpensiveand activities can be designed within the STEM framework. Furthermore, the use of cameras to takephotos of spectra adds a flavor of art, while the opportunity to use useless materials and old devicesfor the activities touches environmental issues.
6. References
1. A guide for making diffraction grating from an optical disk and a list of activities that can bedone, can be downloaded from: http://photodentro.edu.gr/ugc/r/8525/840
2. A guide to build a spectroscope with thin slit that contain a piece of optical disk asdiffraction grating and it is applicable to a camera, as well as detailed examples of its use inchemical analysis and supporting files, can be downloaded from:http://photodentro.edu.gr/ugc/r/8525/841
3. FIT is a file type that contains among others information about the luminosity of each pixelof a digital image. See also at: https://en.wikipedia.org/wiki/FITS
4. FV is an easy to use graphical program for viewing and editing FITS format image or tableand also provides a portal into HERA data analysis service at the HEASARC. FV can bedownloaded from:http://heasarc.gsfc.nasa.gov/docs/software/ftools/fv/
5. A guide for taking spectral profiles using FV can be downloaded from:http://photodentro.edu.gr/ugc/r/8525/841
6. Explanation of the method with many examples can be found at:http://photodentro.edu.gr/ugc/r/8525/841