Light is a Particle!
Introduction to Spectroscopy
Research Question
What can we learn about the microscopic structure of materials from the light
they give off?
Guidelines
We will be constructing homemade spectrometers to investigate the light given
off by a variety of sources including fluorescent, gas discharge and tungsten lamps.
Introduction: Group Discussion
Light can be thought of as a ray which passes straight through a lense or
bounces off of a mirror, as an electromagnetic wave which oscillates through space, or
even as a single particle of energy of a specific color. This single particle is called a
photon.
● Atoms are the smallest building blocks which make
up all things, all matter.
● Atoms are made up of a heavy, positively charged
nucleus and light, negatively charged electrons orbiting
around the nucleus.
● Electrons absorb light in order to stretch farther
away from the nucleus and emit light when they fall back
down toward the nucleus.
● The light emitted by atoms tells us how electrons
move around the nucleus.
Normal light is actually a mixture of a bunch of colors of light, where white light is all the
colors within the visible range. Rainbows, prisms and diffraction gratings split light into
each of its individual colors, showing its spectrum. By looking at the spectrum of light
coming off of a source, we can directly observe qualities about the atom we could never
see directly.
In astronomy, the light we observe through our telescopes is all we have to work with in
studying stars, galaxies, nebula, and planets. Everything we know about astronomy has
come from the spectra of these objects.
Content by: Washington State University OSA-SPIE Student Chapter
Department of Physics and Astronomy
wsu.osahost.org
Equipment:
Pre-cut poster board pieces (6 total)
Diffraction grating square (1 in square, 500 lines/mm)
Paper diffraction scale (printed)
Clear and duct tape
Aluminum foil pieces
Constructing your spectrometer:
The eyepiece of the spectrometer will have the diffraction grating in it, the
spectrometer itself is just a box with a narrow
slit of light allowed in so that the spectrum can
be seen.
1. Construct the eyepiece
a. Take the diffraction grating square and determine which way the line gets
spread out by holding it up to the light.
b. Square the diffraction grating with the eyepiece and mark the diffraction
direction.
c. Tape the diffraction grating over the eyepiece hole.
2. Construct the slit and wavelength scale
a. Tape two straight edges of aluminum foil to the slit opening allowing only a
narrow and straight slit of light through.
b. Tape the wavelength scale so that the light slit is exactly 8.2 cm away
from the first scale line, 400 nm.
3. Assemble the spectrometer pieces, duct tape into place.
Never point spectrometer directly
at the sun or at a laser source!
Observations
Observe each of the light
sources and record your findings.
Sketch the spectrum of each of the
following sources, wavelength in
nanometers.
Content by: Washington State University OSA-SPIE Student Chapter
Department of Physics and Astronomy
wsu.osahost.org
1. Hydrogen
2. Helium
3. Neon
4. Tungsten lightbulb
5. Fluorescent lightbulb
Content by: Washington State University OSA-SPIE Student Chapter
Department of Physics and Astronomy
wsu.osahost.org
6. Laser
(Reflected off of white paper, do not look directly at the laser!)
7. Sun
(Clouds or sunlight reflecting off of white paper, do not look directly at the sun!)
Conclusions
1. What kind of spectra did you observe from atom gas sources? What does this tell
us about the motion of electrons in an atom?
2. If you saw a cloud of glowing gas in your telescope, how might you tell what
kinds of atoms make up that cloud?
3. What kind of spectrum does laser light have?
4. How is the spectrum from a tungsten filament light bulb different from the atom
gas sources?
5. If you look closely at the spectrum of sunlight, you will notice dark lines where the
full rainbow is dimmed. Which of the above gas(es) do many of these lines
correspond to?
Content by: Washington State University OSA-SPIE Student Chapter
Department of Physics and Astronomy
wsu.osahost.org