This document describes the construction and use of an inexpensive webcam-based optical spectrometer for quantitative spectroscopic studies. Key points: - An inexpensive spectrometer was built from readily available materials like DVDs, cardboard, tape and glue to enable students to measure electromagnetic spectra as a function of wavelength within 10s of nm resolution and accuracy. - The spectrometer was calibrated using known emission lines from a helium source and the hydrogen emission spectrum was analyzed, matching theoretical predictions to within 0.04% error. - The low-cost nature of this device makes it suitable for equipping large classes for hands-on spectroscopy experiments and studies in resource-limited educational settings.

1. C O N S T R U C T I O N O F I N E X P E N S I V E W E B -
C A M B A S E D O P T I C A L S P E C T R O M E T E R
U S I N G I M A G E J F O R Q U A N T I T A T I V E
S T U D I E S
Fernando Soares
The Professional Teacher
Dr. Bodi Michael
Spring 2016

2. TABLE OF CONTENTS
 Goals
 Introduction
 Theory
• Atomic Emission
• Spectrograph
 Calibration Methods
 Build your own spectrograph
 Calibration
 Result
 Conclusion

3. INTRODUCTION
• Spectroscopy is an integral part of chemistry and modern physics,
allowing chemists and physics study the structure and properties of
atoms. The webcam spectrograph is a low cost research device which
enables students to measure electromagnetic spectra as a function of
absolute wavelength. Despite their unsophisticated construction and
being made from readily available materials such as DVDs, cardboard,
tape and glue. The webcam spectrographs can resolve spectral line
within 10’s nm resolution and nm accuracy when properly calibrated
from a known source.

4. GOALS:
The purpose of this project is to familiarize students with the optical
workings of a spectrometer and research quality data (which can be
obtained from a commercial spectrometer) and also to compare
experimental data with theoretical predictions.
Understanding the atomic and molecular structure seeing the real
emission spectra in full color as well how to measure wavelengths in the
emission-line
Learn to quickly calibrate a spectrometer using a known spectral source,
and then use this calibration graph and equation to identify unknown
spectral lines

5. THEORY
• Light is electromagnetic radiation. Electromagnetic radiation is
transmitted in a range of waves or particles at different wavelengths and
frequencies. This broad range of wavelengths is known as the
electromagnetic spectrum.
E=h.γ
λ=
∁
𝛾
Electromagnetic spectrum
λ - Wavelength in nm
c- The speed of light in m/s
γ - Frequency in s-1
E- is a Energy
h - is a Planck’s constant (6.6*10-34 J.s)
𝛾- is a frequency of the electromagnetic wave

6. ATOMIC EMISSION SPECTRA
• Bohr atomic model predict, that electrons in atoms “are found in only
certain allowed stationary states (lowest energies states possible) with
well-defined energies”2. However, the electrons can be excited to the
high energy states (levels) when just the atom absorb the right
frequency to generate a photon whose energy equals the energy
difference between the states. The electrons then return to lower states
initially transited emitting energy in a form of light, with each atom or
molecule releasing a single photon of light for each electron energy
transition it makes.
Transitional hydrogen atom

7. • Hydrogen Emission spectrum line (Balmer series for hydrogen Atom )
• Color and shells involved in the downward transition of Balmer series.

8. SPECTROGRAPH
• The spectrograph is a research device which is used to measure the intensity of
electromagnetic radiation at a different wavelength. In its most basic form, the device consists
of an opaque barrier with a slit in it (to define the beam of light) a diffraction grating (to split
the beam of light into its component colors), and an eyepiece or screen (to allow the user to
view the resulting spectrum).
Diffractiongratingdiagram
 Diffraction grating is the heart of the spectrometer,
consist of
many parallel evenly spaced mirrored slits on an opaque
sheet. The slit spread the light into different color that make its
possible to be measured as function of wavelength .
• The basic function of spectrograph are: A narrow beam of light enters the spectrograph
through a small slit in the barrier; the light passes through a diffraction grating and its
split into its component colors; the vertical lines is projected onto the screen.

9. CALIBRATION METHODS
• The atomic spectrum will be analyzed by a powerful scientific analysis image software called
ImageJ designed by Wayne Rasband a Special Volunteer at National Institutes of Mental
health (NIH) Bethesda, Maryland, USA. ImageJ is public domain open source software, can
run as an online applet or as a downloadable application on any computer with a Java 1.5 or
later virtual machine.
• Calibration is performed by using statistical models that describe the relationship between
dependent and independent variables. Linear regression is a mathematical technique to see
deviations from a straight line, fit linear relations and express the relationship between the
experimental result and quantities predicted by theory.
• Linear regression is used to study the linear relationship between a dependent variable Y
(wavelengths) and independent variables [Distance (Pixels)].
• There is an analytic expression for the slope and intercept and their uncertainties for a
straight-line fit, defined by equation Y=bX+a, where a is the y- coordinate intercept, and b is
its slope. However, the parameters a and b, of the regression line are estimated from the
values of the dependent variable Y(wavelengths), and independent variable X[Distance
(Pixels)] with the aid of a statistical model.

10. BUILD YOUR OWN SPECTROGRAPHMaterials needed
The light entrance slit
View port Grating hold
piece
G. hold piece folded and shaped with
tape

11. Making a grating from DVD
Grating
Grating attach to the grating holder Align slit with center of grating
Complete
spectrometer

12. CALIBRATION
1. Take a picture of helium gas with room lamp
off.
2. Open ImageJ to convert image to data file
Helium spectral linesHelium gas discharge
Plotted intensity against pixels
3. Using data to compare intensity/position to an intensity/ wavelength source available from NIST. Using EXCEL
least square fitting algorithm we generated a calibration which calibrated our x pixel value to a wavelength
angstrom (and nm).

13. Pixels Wavelengths
511 3888.6489
541 4026.191
632 4471.479
680 4713.146
721 4921.931
740 5047.74
908 5875.6148
1070 6678.1517
1151 7065.1771
y = 4.9952x + 1327.9
R² = 0.9999
0
1000
2000
3000
4000
5000
6000
7000
8000
0 200 400 600 800 1000 1200 1400
Wavelength(Ang.)
Distance (Pixels)
Linear regression Calibration -Helium
Using EXCEL least square fitting algorithm we generated a calibration which calibrated our x pixel value to a
wavelength angstrom (and nm).

14. RESULT
• Used a linear fit configuration against 650 nm red laser to test calibrations.
648nm
• We found our peak values of intensity appeared at 648nm which lets us estimate our accuracy
of +/-2nm and a resolution of approximately +/- 80 nm from the full width at half height.

15. • Using Calibration to analyze the hydrogen emission comparing with Balmer hydrogen emission
lines theory
Hydrogen spectral lines obtain with spectrometer
Theoretical Observed
λ(nm) Color Shells Involved λ(nm) Color
656.4 Red 3→2 651.8 Red
486.1 Blue (cyan) 4→2 482.9 Blue (cyan)
434.2 Blue 5→2 430.9 Blue
410.2 Violet 6→2 . Violet
Our calibration present an error of 0.041144 % off the expected value which mean that could be
used to identify unknown elements with certain accuracy.
0
20
40
60
0 200 400 600 800
Intensity(Grayvalue)
Wavelenght(nm)
Hydrogen Sample
651.8nm

16. CONCLUSION
• An inexpensive cardboard visible spectrometer has been constructed and found to be a
useful tool for teaching spectroscopy to high school and undergraduate students. The web-
cam based spectrometer yielded quantitative wavelength measurements that agreed well
with theory to +/- 2 nm accuracy and +/- 80 nm resolution. The measurement of the
wavelength of highest pixels number of the hydrogen spectral line is 0.041144% off by the
expected value. The inexpensive nature of the device, costing an order of magnitude less
than comparable commercial devices, makes it an appealing option for supplying
spectrometers to large physics and chemistry classes for use in laboratory experimentation or
in resource-limited educational settings.

17. REFERENCE LIST• 1- Chaisson, E., & McMillan, S. (2005) Astronomy Today. 5th ed. Upper Saddle River, New Jersey 07458
• 2- Ferreira T., & Rasband W. (2012) ImageJ User Guide (IJ 1.46r Revised edition) Retrieved from
https://imagej.nih.gov/ij/docs/guide/user-guide.pdf
• 3- Hughes, I.G., & Hase,T.P.A.( 2010). Measurements and their Uncertainties. A Practical Guide to Modern Error Analysis.
Oxford University Press inc., New York.
• 4- Harris, R. (1998). Modern Physics. 2nd ed.
• 5- Introduction to spectroscopy- Physics & Astronomy
• http://www.phy.olemiss.edu/Astro/Ex_IndoorLab.pdf
• 5- Lucas, J. (2015, March 12). What Is Electromagnetic Radiation? LiveScience Retrieved
from http://www.livescience.com/38169-electromagnetism.html
• 6- Physics, C. () Bohr’s Theory of the Hydrogen Atom. Retrieved from
• http://philschatz.com/physics-book/contents/m42596.html
• 7- Redd, N. (2013, November 26). Make Your Spectroscope| Spectroscopy Science Fair Project. Livescience Retrieved from
• http://www.livescience.com/41548-spectroscopy-science-fair-project.html
• 8- Schneider, A., Hommel, G., & Blettner, M., (2010). Linear Regression Analysis. Journal Deutsches Arzteblatt 107(44): 776-
782. doi: 10.3238/arztebl.2010.0776. Retrieved from,
• http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2992018/
• 9- Stark, G.(2011) Optical Spectrum; Visible radiation; Visible spectrum. ENCYCLOPEDIA BRITANNICA Retrieved from
• http://www.britannica.com/science/light/Unpolarized-light#toc258433
• 10- Stacy, Palen …et. al. (2012). Understanding our Universe (1st ed.)