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Emission Spectra
“The Elements”
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Vocabulary
Atom
Element
Spectrum (any of the following types of spectrum listed below)
Electromagnetic spectrum (EM)
Element
Molecule
Wavelength
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Vocabulary
All definitions are from http://dictionary.reference.com
Atom
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A unit of matter, the smallest unit of an element, having all the characteristics of
that element and consisting of a dense, central, positively charged nucleus
surrounded by a system of electrons. The entire structure has an approximate
diameter of 10-8 centimeter and characteristically remains undivided in chemical
reactions except for limited removal, transfer, or exchange of certain electrons.
This unit regarded as a source of nuclear energy.
Element
 A substance that cannot be reduced to simpler substances by normal chemical
means and that is composed of atoms having an identical number of protons in
each nucleus.
 Any of more than 100 fundamental substances that consist of atoms of only one
kind and that singly or in combination constitute all matter
 Each element emits a unique spectrum. These elements can be identified by their
wavelengths in nanometers.
http://hyperphysics.phy-astr.gsu.edu/hbase/vision/specol.html#c1
Emit
to give off or send out (the process is called emission)
Energy :
the ability to do work; light is a form of energy
Light
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Electromagnetic radiation that has a wavelength in the range from about 4,000
(violet) to about 7,700 (red) angstroms and may be perceived by the normal
unaided human eye.
 Common term for electromagnetic radiation of any wavelength
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The Spectrum of Visible Light
The visible part of the spectrum may be further subdivided according to color, with red at
the long wavelength end and violet at the short wavelength end, as illustrated
(schematically) in the following figure.
The visible spectrum
http://csep10.phys.utk.edu/astr162/lect/light/spectrum.html
http://www.nsta.org/main/news/stories/science_teacher.php?news_story_ID=48612&print=yes
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Molecule:
The smallest particle of a substance that retains the chemical and physical properties of
the substance and is composed of two or more atoms; a group of like or different atoms
held together by chemical forces. A molecule will emit a spectrum from the combination
of elements that it possesses.
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(Physics) The smallest part of any substance which possesses the characteristic
properties and qualities of that substance, and which can exist alone in a free state.
 (Chem.) A group of atoms so united and combined by chemical affinity that they
form a complete, integrated whole, being the smallest portion of any particular
compound that can exist in a free state; as, a molecule of water consists of two
atoms of hydrogen and one of oxygen. Cf. Atom.
Spectrum
The distribution of a characteristic of a physical system or phenomenon, especially:
 The distribution of energy emitted by a radiant source, as by an incandescent
body, arranged in order of wavelengths.
 The distribution of atomic or subatomic particles in a system, as in a magnetically
resolved molecular beam, arranged in order of masses.
 The distribution of a characteristic of a physical system or phenomenon,
especially the distribution of energy emitted by a radiant source arranged in order
of wavelengths.
 The color image presented when white light is resolved into its constituent colors:
red, orange, yellow, green, blue, indigo, violet.
 The plot of intensity as opposed to wavelength of light emitted or absorbed by a
substance, usually characteristic of the substance and used in qualitative and
quantitative analysis.
 The distribution of atomic or subatomic particles in a system, as in a magnetically
resolved molecular beam, arranged in order of masses.
 a continuum of color formed when a beam of white light is dispersed (as by
passage through a prism) so that its component wavelengths are arranged in order
 any of various continua that resemble a spectrum in consisting of an ordered
arrangement by a particular characteristic (as frequency or energy
ELECTROMAGNETIC SPECTRUM
(2) : MASS SPECTRUM c : the representation (as a plot) of
a spectrum.
(a)The several colored and other rays of which light is composed, separated by the
refraction of a prism or other means, and observed or studied either as spread out on a
screen, by direct vision, by photography, or otherwise. (b) A luminous appearance, or an
image seen after the eye has been exposed to an intense light or a strongly illuminated
object. When the object is colored, the image appears of the complementary color, as a
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green image seen after viewing a red wafer lying on white paper. Called also ocular
spectrum.
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Absorption spectrum, the spectrum of light which has passed through a medium
capable of absorbing a portion of the rays. It is characterized by dark spaces,
bands, or lines. The electromagnetic spectrum, broken by a specific pattern of
dark lines or bands, observed when radiation traverses a particular absorbing
medium. The absorption pattern is unique and can be used to identify the material.
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Chemical spectrum, a spectrum of rays considered solely with reference to their
chemical effects, as in photography. These, in the usual photogrophic methods,
have their maximum influence at and beyond the violet rays, but are not limited to
this region.
Chromatic spectrum, the visible colored rays of the solar spectrum, exhibiting the
seven principal colors in their order, and covering the central and larger portion of
the space of the whole spectrum.
Continous spectrum, a spectrum not broken by bands or lines, but having the
colors shaded into each other continously, as that from an incandescent solid or
liquid, or a gas under high pressure.
Diffraction spectrum, a spectrum produced by diffraction, as by a grating.
Emission Spectrum, an electromagnetic spectrum that derives its characteristics
from the material of which the emitting source is made and from the way in which
the material is excited.
Gaseous spectrum, the spectrum of an incandesoent gas or vapor, under moderate,
or especially under very low, pressure. It is characterized by bright bands or lines.
Normal spectrum, a representation of a spectrum arranged upon conventional plan
adopted as standard, especially a spectrum in which the colors are spaced
proportionally to their wave lengths, as when formed by a diffraction grating.
Ocular spectrum. See Spectrum
Prismatic spectrum, a spectrum produced by means of a prism.
Solar spectrum, the spectrum of solar light, especially as thrown upon a screen in
a darkened room. It is characterized by numerous dark lines called Fraunhofer
lines.
Spectrum analysis, chemical analysis effected by comparison of the different
relative positions and qualities of the fixed lines of spectra produced by flames in
which different substances are burned or evaporated, each substance having its
own characteristic system of lines.
Thermal spectrum, a spectrum of rays considered solely with reference to their
heating effect, especially of those rays which produce no luminous phenomena.
Electromagnetic spectrum (EM):
the entire range of wavelengths or frequencies of electromagnetic radiation
extending from gamma rays to the longest radio waves and including visible light
Mass Spectrum: the spectrum of a stream of gaseous ions separated according to
their mass and charge.
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Spectroscope
An optical instrument for forming and examining spectra (as that of solar light, or those
produced by flames, in which different substances are volatilized), so as to determine,
from the position of the spectral lines, the composition of the substance. The spectrum of
an element may also be produced by exciting the electrons of the element by passing
electricity through it in a vacuum.
Wavelength
The distance between one peak or crest of a wave of light, heat, or other energy and the
next corresponding peak or crest.
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“Chemical Detective activity”
Identifying the elements through emission spectra
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Objective
Students identify substances based on the visible spectra they emit, gaining familiarity
with discrete spectra and their relationship to chemical elements.
Precautions:
Power Sources for gas lamps are a very high voltage. EXTREME CAUTION
SHOULD BE USED TO PLUG AND UNPLUG. STUDENTS SHOULD NOT
TOUCH THE LAMPS DIRECTLY. ALWAYS TURN OFF POWER SOURCE
AND UNPLUG BEFORE CHANGING THE GAS BULB. The lamps should be on
for minimum lengths of time to conserve bulb life.
Related Subjects:
Astronomy
Physical Science
Chemistry
Students should already know:
Vocabulary terms above
That each element emits a unique wavelength of light
Basic use of a spectroscope (see directions on insert of sprectroscopes)
Introduction:
When you listen to the radio, cook dinner in a microwave, or watch TV you are using
electromagnetic waves. Radio waves, television waves, and microwaves are all types of
electromagnetic waves. They only differ from each other in wavelength. Wavelength is
the distance between one wave crest to the next.
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Wavelength
Crest
Trough
Waves in the electromagnetic spectrum vary in size from very long radio waves the size
of buildings, to very short gamma-rays smaller than the size of the nucleus of an atom.
http://imagers.gsfc.nasa.gov/ems/waves3.html
Electromagnetic waves can not only be described by their wavelength, but also by their
energy and frequency? All three of these things related to each other mathematically.
This means that it is correct to talk about the energy of an X-ray or the wavelength of a
microwave or the frequency of a radio wave.
The electromagnetic spectrum includes, from longest wavelength to shortest: radio
waves, microwaves, infrared, optical, ultraviolet, X-rays, and gamma-rays.
Visible light/ optical waves are the only electromagnetic waves we can see. We see these
waves as the colors of the rainbow. Each color has a different wavelength. Red has the
longest wavelength and violet has the shortest wavelength. When all the waves are seen
together, they make white light.
In a rainbow or the separation of colors by a prism we see the
continuous range of spectral colors, the visible spectrum.
A spectral color is composed of a single wavelength and
can be correlated with the wavelength as shown on a EM chart.
Purpose:
The purpose of this laboratory assignment is to explore the visual electromagnetic
spectrum using a spectroscopes and gas tubes.
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An electromagnetic spectrum is an arrangement of electromagnetic waves
according to wavelength and frequency.
To realize that each element/gas emits a unique spectrum.
Identify these elements/gases by analyzing the spectrum that they emit.
Realize that stars are composed of various elements, usually the lighter elements,
and these can also be identified by their spectrum.
Materials
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Overhead projector, holographic diffraction grating, and two pieces of 8” × 10”
dark paper;
Hand-held diffraction gratings or hand-held spectroscopes;
Various light sources (light sources with a long thin tube or filament are easier to
view):
• incandescent bulb (creates a continuous spectrum);
• fluorescent tube (coated tubes yield a seemingly continuous spectrum);
• “black light” tube (uncoated tube for creating a discrete spectrum);
• gas spectrum tubes for different elements, include neon if possible (gas spectrum
tubes create discrete spectra); and
• gas spectrum tube power supply;
Activity Sheet A: “Visible spectra for chemical elements” (Figure 1);
Activity Sheet B: “Chemical Detective” (Figure 2);
Colored pencils, markers, or crayons.
Safety
Caution students not to touch the light sources as they may be hot and the gas tubes
use high voltages. Students should not insert the gas spectrum tubes in the power supply
or change the gas spectrum tubes. Students should not stare directly at the light sources
for extended periods of time.
Procedure
1. In a darkened room, use the overhead projector, the holographic
diffraction grating, and the two pieces of dark paper to project a
continuous color spectrum on a wall or screen following the detailed
instructions given in “The Visible Spectrum” activity on the back of The
Electromagnetic Spectrum poster.
2. Ask students to describe what they see and make a colored drawing in the
space provided. Students may compare the spectrum with a rainbow or
with light seen through a prism or crystal. If desired, explain that the
diffraction grating separates the light according to wavelength.
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The activity
1. Hold the hand-held diffraction gratings or spectroscopes to your eye. In a
darkened room, view the incandescent source through their gratings (or
spectroscopes).
2. Record observations.
3. View the sources that produce a discrete spectrum (the black light and one of the
gas tubes, saving the neon tube for step 2 below).
4. Light source will be turned on around the room at various locations for student
viewing. DO NOT TOUCH THEM OR ATTEMPT TO TURN THEM OFF!.
5. Draw the spectra you see and explain how the spectra produced by the black light
and the gas tube differ from the one produced by the incandescent light.
6. Describe any relationship that might exist between the colors viewed in the
spectrum and the appearance of the light source to our eyes (white light has all
colors; black light has purple, blue, and green but not much orange or red; a
hydrogen tube looks purple and has purple, blue, and red).
7. Consider electromagnetic fingerprints and discuss why they are important in
identifying individual elements. Spectra are analogous to fingerprints: Each
chemical element and molecule produces a unique pattern of spectral lines. This
pattern of lines can be used to identify the presence of a particular element or
molecule in an unknown substance.
8. Identity, illuminate the following gas tubes positioned around the room and justify
your predictions.
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9. Use the following chart to help you identify the spectra for the various elements
and have match the lines they see from the neon gas tube to the chart.
10. Describe how you would use the previous investigation to determine what
elements might be burning from the flame colors or what elements a star might be
made of.
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Assessment
Arrange students into new groups. Give each group a copy of Figure 2. Have each group
work as a team to solve the mystery and submit a written report discussing their solution,
the evidence they gathered that led them to the solution, and how they used spectroscopic
techniques to solve the crime. Consider stressing that more than one “criminal element”
was involved. Note that the “aliases” of the criminal elements are their chemical symbols,
and the “perpetrators” are argon and sodium.
Reinforcing concepts
The light that we see with our eyes represents only a small portion of the electromagnetic
spectrum. Developing the technology to detect and study other portions of the
electromagnetic spectrum has had a tremendous impact on astronomy, where scientists
must use the properties of light to learn about objects that are too far away to visit.
NASA educational materials use astronomical data and the excitement of space
exploration to reinforce fundamental science concepts such as the electromagnetic
spectrum and motivate interest in science and technology.
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Assignment:
Use colored pencils or crayons to complete the following assignment.
1. Draw the colors of the spectra you see in Incandescent Light
2. Explain how the spectra produced by the black light and the gas tube differ from
the one produced by the incandescent light.
3. Draw the colors of the spectra you see in the gas tube.
4. What is your hypothesis as to the elemental gas found in the tube?
5. Draw the colors of the spectra you see in the gas tube.
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6. What is your hypothesis as to the elemental gas found in the tube?
7. Draw the colors of the spectra you see in the gas tube.
8. What is your hypothesis as to the elemental gas found in the tube?
9. Draw the colors of the spectra you see in the gas tube.
10. What is your hypothesis as to the elemental gas found in the tube?
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11. Draw the colors of the spectra you see in the gas tube.
12. What is your hypothesis as to the elemental gas found in the tube?
13. Draw the colors of the spectra you see in the gas tube.
14. What is your hypothesis as to the elemental gas found in the tube?
15. Draw the colors of the spectra you see in the gas tube.
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16. What is your hypothesis as to the elemental gas found in the tube?
17. Draw the colors of the spectra you see in the gas tube.
18. What is your hypothesis as to the elemental gas found in the tube?
19. Draw the colors of the spectra you see in the gas tube.
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20. What is your hypothesis as to the elemental gas found in the tube?
21. Which of the previous element/gases would you most likely find in our Sun, a
medium sized and aged star?
22. Draw the probable spectrum lines for our Sun.
23. What might the spectrum lines look like for a very old star, such as a red giant?
24. What would be the main element/gas of the red giant?
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Teacher’s Page
PA Assessment Standards:
Physical Science, Chemistry and Physics
3.4.7A Describe concepts about the structure and properties of matter.
3.4.7B Relaate energy sources and transfers to heat and temperature.
3.4.7D Describe essential ideas about the composition and structure of the u
niverse and earth’s place in it.
3.4.10D Explain essential ideas about the composition and structure of the
universe.
Technological Devices
3.7.7 Use appropriate instruments and apparatus to study materials.
3.7.10 Apply appropriate instruments and apparatus to examine a variety of
objects and processes.
Preparation:
Show students the incandescent light source, the black light source, and one of the
gas tubes other than neon. (To work with gas spectrum tubes, follow the
manufacturer’s directions. Gently insert the tube into the power supply. Then,
briefly turn the power supply on to illuminate the gas. Turn the power supply off
immediately after student viewing to prolong the life of the tube.) Briefly turn on
each source so students can see the color of the light, while instructing students
not to stare directly at the light sources for long periods of time. Turn each source
off after it has been viewed. Ask students to list three to five questions they have
about what they see. Discuss that they will use the diffraction gratings (or
spectroscopes) to view the light from each source and ask them to predict whether
each light source’s spectrum will be similar to or different from that of the
overhead projector
Students should reconfirm that white light can be diffracted into a continuous
color spectrum as was demonstrated at the beginning of the activity.
Follow directions provided with the spectroscopes and gas tubes and power
source!
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The electromagnetic spectrum
Light, or electromagnetic radiation, comes in many forms. There are radio waves, microwaves,
infrared light, visible light, ultraviolet light, X-rays and gamma rays, all of which form what is known
as the 'electromagnetic spectrum'
The electromagnetic spectrum is subdivided into seven regions according to wavelength. Each
portion of the spectrum interacts with matter in a slightly different way and is given a different
name. From longest to shortest wavelength the seven divisions are:
Radio (wavelengths greater than 0.3 metres)
Earth's atmosphere hides most electromagnetic radiation from space except visible light, certain
infrared frequencies and radio waves. For this reason, we can place radio telescopes on Earth's
surface and radio astronomy was the first non-optical study of radiation from space. A number of
the most massive galaxies were found to be extremely powerful sources of radio waves. Radio
astronomy led to the discovery of pulsars which pulse regular radio emissions.
Microwaves (wavelengths between 1 millimetre and 0.3 metres)
Earth's atmosphere begins to shield radiation from us. The most important form of microwave
radiation in astronomy is called the Cosmic Microwave Background (CMB). Discovered in 1965, CMB
comes from all parts of the Universe with the same intensity. CMB became solid evidence for the
'Big Bang' theory, which predicted that the shockwave of the primeval explosion would be still
detectable. ESA's Planck mission will study the CMB and thus will be seeing the Universe as it was
almost at its beginning.
Infrared (wavelengths between 700 nanometres – 1 millimetre)
The primary source of infrared radiation is heat. The higher the temperature, the faster the atoms
and molecules in an object move and the more infrared radiation. The first infrared space mission
was IRAS (Infrared Astronomical Satellite) which detected about 350 000 infrared sources. Later,
ESA's Infrared Space Observatory (ISO) made important studies of the dusty regions of the
Universe. ESA's Herschel mission will build on this work.
Visible (wavelengths between 400 – 700 nanometres)
Until 1945, most astronomy was optical. This meant studying a very small range of wavelengths. It
is from these optical wavelengths that most people derive their picture of the Universe, dominated
by bright stars and galaxies. Visible light is predominantly released by objects between 2000 and 10
000°C. The NASA/ESA Hubble Space Telescope has a powerful optical telescope on board which
enables it to take stunning photographs in real colour.
Ultraviolet (wavelengths between 10 – 400 nanometres)
As soon as observations from above the atmosphere became possible, the classical techniques of
optical astronomy were extended into the ultraviolet. The Sun and other hot objects are sources of
ultraviolet radiation. In 1978, the International Ultraviolet Explorer (IUE) was launched. IUE
dominated ultraviolet space astronomy for nearly two decades. It generated spectra showing
intensities at different wavelengths from selected objects in the sky. Temperatures, motions,
magnetism and chemical composition are all discernible in the ultraviolet spectra.
X-rays (wavelengths between 0.01 – 10 nanometres)
Most of the observable matter in the Universe today is in a hot state, radiating short-wavelength
radiation and X-rays. Massive clouds of gas at a very high temperature fill the spaces between
galaxies. Whenever a new star is formed, a collapsing cloud of gas reaches temperatures sufficient
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for nuclear reactions to start, powering the star. Conditions in the primeval Universe were very
different - with only a few pre-existing molecules and no dust available for cooling, only the most
massive clouds could collapse. They would make not stars, but black holes. Theorists suspect that
giant black holes may have been among the earliest objects created in the Universe and would have
produced X-rays. Two ESA missions, XMM-Newton and XEUS are designed to observe these X-rays.
Gamma rays (wavelengths less than 0.01 nanometres)
Gamma rays from space are blocked by the Earth’s atmosphere – fortunately for us, because this
powerful radiation is lethal. Gamma-ray telescopes in space give evidence for the processes that
made the Universe habitable. When a massive star has used up its hydrogen fuel, it ends in a
supernova explosion, emitting gamma rays. During this explosion, radioactive elements are formed
and ejected into space, decaying or combining to form the other elements. ESA's COS-B satellite
(1975-1982) created a catalogue of gamma-ray sources. ESA's Integral spacecraft, launched in
2002, takes this work forward, studying the phenomenon known as 'gamma-ray bursts'.
http://www.esa.int/esaSC/SEM0W1T1VED_index_0.html
Observations: Seeing in visible wavelengths
Even a casual glance into a clear night atmosphere reveals
that at visible wavelengths, stars dominate our surrounding
sky. Visible light is the predominant electromagnetic radiation
released by objects with temperatures of between 2000 and
10 000°C.
Orion Nebula's Trapezium cluster
Stars come in a variety of masses, with the vast majority
containing between one tenth and ten times the mass of our
Sun. The different masses determine how efficiently they
generate energy and this gives rise to the surface
temperature. Lower temperature stars shine with red light
and high-temperature stars are blue or white. Being yellow,
our Sun is a middle temperature star measuring around
6000°C.
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All the stars visible to the naked eye are part of our galaxy, the
Milky Way. However, thousands of millions of other galaxies
stretch throughout space and these are mostly studied using
visible wavelengths.
The visible wavelengths are also the realm of the emission
nebulae. They are glowing clouds of gas and often form some of
the most breathtaking objects in the Universe, most often
appearing red. This color comes from the predominant emission
from nebulae, which is hydrogen gas.
Because of the nature of the structure of the hydrogen atom,
when it releases energy it does so efficiently at a specific
wavelength of red light (656 nanometres).
NGC 2264, Cone Nebula
These are mostly clouds of gas that surround young, massive stars but
some emission nebulae are the death shrouds of old stars. These are
historically, but confusingly, called 'planetary nebulae'. Exploding stars also
create emission nebulae known as ‘supernova remnants’.
Eye-catching celestial
helix
The most common way for astronomers to analyse visible light from a
celestial object is to split it into its constituent wavelengths to form a
spectrum. Studying this allows astronomers to analyse the composition and
physical condition of the celestial object under consideration.
If they are close to a star, dust clouds can reflect visible light. Such clouds usually create blue
patches in space, similar to the colour of our daytime sky.
http://www.esa.int/esaSC/SEMNFEX5WRD_index_0.html
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The following activities are from FUSE, a joint project of the National
Aeronautics and Space Administration and the Johns Hopkins University in collaboration
with:
Centre National d'Etudes Spatiales (France), the Canadian Space Agency, the University
of Colorado, and the University of California, Berkeley.
http://fuse.pha.jhu.edu/overview/mission_ov.html
They have been reprinted with permission.
Exploring Our Universe:
From the Classroom to Outer Space
I. Spectroscopy
Activity #6
SPECTROSCOPY:
CHEMICAL DETECTIVE
NOTES TO THE
TEACHER
Grades 8 and up
Level:
Objectives: Students will explain the process of dispersion, and will identify substances
based on the visible spectra they emit.
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Materials:
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Triangular prisms
Hand-held diffraction gratings
Various light sources: (Note: if the light source is a long thin tube or
filament, you can avoid the need to put a slit in front of the source.)
o
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Incandescent bulbs (continuous spectrum)
fluorescent tubes (coated tubes yield a seemingly continuous
spectrum)
o "black light" tube (uncoated tube for discrete spectrum)
o spectrum tubes for different elements (discrete spectra)
Visible spectra for various chemical elements (see attached handout)
"Chemical Detective" activity (see attached handout)
Procedures: [NOTE: students should have previous exposure to the electromagnetic
spectrum and to the concepts of wave refraction and interference.]
1. Use a prism or diffraction grating with an incandescent bulb to
project a continuous color spectrum on a wall or overhead screen.
Explain that the light is being dispersed, or separated according to
wavelength. Have students identify the colors present in the
spectrum; explain that there is no set number of colors in the
spectrum, but that it is a continuous range of colors.
2. Give students hand held diffraction gratings. Have them view an
incandescent source to reconfirm that white light can be separated
into a continuous color spectrum. Next have them view a source
which produces a discrete spectrum (gas tube, "black light") and
have them explain how the spectrum they see is different. Ask them
to describe any relationship that might exist between the colors
viewed in the spectrum and how the light source looks to our eyes
(white light has all colors, "black light" has purple, blue and green
but not much orange or red).
3. Ask students to consider fingerprints and explain why they are
important. Tell them that spectra can be used just like fingerprints:
each chemical element and compound produces a unique pattern of
spectral lines. This pattern of lines can be used to identify the
presence of a particular element or compound in an unknown
substance. Without telling them its identity, illuminate a neon gas
tube. Ask students to guess what is in the tube; have them justify
their guesses. Have students view the neon gas tube through their
diffraction gratings and record the number of spectral lines they
view and the color of each line. See whether students notice a
relationship between the colors of the spectral lines and the color of
the light our eye sees (most of neon's emission lines in the visible
range are red and orange, so neon appears red). Give students a copy
of the handout "Elemental Spectra" showing visible spectra for
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various elements and have them match the lines they see from the
gas tube to the c
4. Arrange students into groups. Give each group a copy of the activity
"Chemical Detective." Have each group work as a team to solve the
mystery and submit a written report discussing their solution, the
evidence they gathered that led them to the solution, and how they
used spectroscopic techniques to solve the crime.
Discussion: All secondary school physical science texts discuss the phenomenon of light
dispersion. High school physics texts usually include a mathematical
description of the process by which different wavelengths of light can be
separated. Yet the texts seldom offer students activities that reinforce these
concepts. This is unfortunate, since a demonstration of spectroscopy
techniques almost always produces an "oh, wow!' response. The viewing of
a spectrum- a rainbow of colors- is always a memorable experience; it is
also a vivid example of light's wave-like properties.
1. Give students diffraction gratings to take home. Have them observe
Extensions:
light sources in their neighborhood (street lights, business signs,
etc.) For each light source they observe, have them record whether
the spectrum they viewed was continuous or discrete. For discrete
spectra, have students record the number of lines viewed, and the
colors of the lines. Have students use the sample spectra from
various chemical elements to identify the composition of the light
source. (NOTE: there are charts listing the visible spectra for typical
light sources such neon, metal halide, sodium vapor and mercurysee Sources.
2. Discuss how a diffraction grating works. Develop the equation
relating the wavelength of colors in a spectrum to the dispersion
angle and the spacing of the lines on the diffraction grating [ = d
sin ]. If available, use spectrographs to measure wavelengths of
simple spectral lines.
3. Have students who have learned triangle trigonometry do Activity
#4 in Kit II: Tracing Light Through - Understanding Diffraction.
This activity teaches the principles on which the FUSE spectrometer
is based and tests understanding by asking students to trace light
rays from a star through the spectrometer.
4. Have students research the process by which rainbows are formed,
and explain the conditions necessary for viewing them.
5. Have students contact fluorescent light manufacturers (check
websites like www.sylvania.com or www.ge.com) to find out how
fluorescence works and what techniques they use to make
fluorescent lights produce a spectrum similar to natural light
(sunlight). Also, they can investigate what type of lighting is most
appropriate for different situations, and how this relates to the
spectral emissions.
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Sources:
Flinn Scientific, 1-800-452-1261 (for hand held diffraction gratings)
Electro-Technic Products, Inc., 773-561-2349 (for gas spectrum tubes)
Arbor Scientific, 1-800-367-6695 ("Night Spectra Quest" chart for
identifying typical light sources)
CHEMICAL DETECTIVE
STUDENT ACTIVITY
You are a private eye who stays in business mainly by recovering lost dogs and the
occasional runaway pet turtle. You have just learned that last night some devious criminal
elements pulled a huge bank robbery. This could be your big break. Crack this case and
you'll be famous!
You grab your diffraction grating and head to the scene of the crime. What is that strange
glowing gas you see in the bank vault? Hold your breath, it's a clue. You look at the gas
through the grating. The emission lines you see are like fingerprints. Now you can
identify the criminal elements.
This is the "perpetrator spectrum":
Look at the visible light emission lines of the suspects, shown on the following page. Can
you match the lines in the "perpetrator spectrum" to the elements whodunnit?
The president of the bank is offering a huge reward to whoever solves this case but is
demanding hard evidence against the wrongdoers. Write a report to the president of the
bank listing the names and aliases of the perpetrators and, most importantly, explaining in
detail how you used techniques of spectroscopy to crack the case.
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Cosmic Barcodes
Text by Ken Sembach and Bill Blair
Graphics by Ken Sembach
Astronomers learn about the Universe by observing light from distant astronomical
objects, like stars or galaxies. Light contains information, and since it is much easier to
observe a star than it is to travel to one, there is clearly a benefit to being able to
understand what the light is telling us!
One of the main tools for studying light is a device called a spectrograph, which breaks
light into its component colors, much like raindrops refract sunlight to produce beautiful
rainbows in the sky. When attached to a telescope, a spectrograph becomes a powerful
tool for learning about the Universe.
Luckily for astronomers, this technique can be used with all kinds of light, not just the
visible light that our eyes are sensitive to. Different kinds of light, like infrared,
ultraviolet, X-ray light, etc., contain different kinds of information. The FUSE satellite
uses light in the far-ultraviolet spectral region, light having wavelengths between 90 and
120 nanometers (1 nanometer = 1 billionth of a meter!). For comparison, visible light
ranges from about 400 to 700 nanometers (4000 to 7000 Angstroms).
In the absence of any intervening material, the light from a star reaches us unobscured.
When the light is dispersed into colors by a spectrograph, it may look something like this
continuous spectrum, which has a smooth, gradual change of color, and no breaks or
dropouts in the intensity of the light:
However, if there are one or more gas clouds between us and the star, this interstellar
medium absorbs some of the light before it reaches us. Depending upon what types of
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atoms or molecules are present in the absorbing gas clouds, a number of dark features, or
absorption lines, are superimposed on the continuous spectrum emitted by the star,
something like this:
These absorption lines contain information about the composition of the clouds (the kinds
and relative amounts of atoms and molecules in the gas). They also tell us such things as
how much gas is in the clouds, the gas density, the temperature of the gas, how fast it is
moving toward or away from us, whether there are cold regions embedded in warmer
material, and whether there are interstellar dust grains mixed in with the gas. All this
from analyzing the light!
These absorption features can be thought of as cosmic barcodes, with each type of atom
or molecule producing a different barcode signature. One can then think of a
spectrograph as a "barcode reader". Once the barcode produced by a gas cloud has been
read, astronomers can interpret what the barcode means. Here are examples of the types
of barcodes that are produced by the FUSE spectrographs:
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Now it's YOUR turn!
See if you can guess which elements have left their mark on this spectrum:
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The Redshift Explained
The above diagram shows the spectrum (component colors) of a galactic star. The different
wavelengths(the distance from one wavecrest to the next) of light are what human eyes see as
colors. The shortest wavelengths appear at the blue end of the spectrum. The longest wavelengths
appear at the red end of the spectrum. The numbers on the top measure wavelength in
nanometers. The deep black lines in the color spectrum are absorption lines. Each chemical
element in a star's atmosphere absorbs a certain color. By looking at the absorption lines in a
spectrum, we are able to determine what elements are present in a stars atmosphere (the missing
colors are the colors that the elements in the stars atmosphere absorb).
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Notice how the pattern of absorption lines shifts from the blue end to the red end as the galatic
star becomes fainter. This is known as the Red Shift.
The Doppler Effect is used to explain the Red Shift. The Doppler Effect states that if a source that
is emitting waves moves away from us, the wavelength of the waves we recieve from it will be
longer. This implies that stars moving away from us will be red shifted(light with longer
wavelength appears at the red end of the spectrum). In the 1920's, Edwin Hubble discovered that
many galaxies appeared red shifted. This means that these galaxies are moving away from us!
The universe is expanding! The idea that the universe is expanding supports the big bang theory.
Here are a few explainations of the Red Shift which do not support the big bang. *The following
comes from CREATION-EVOLUTION ENCYCLOPEDIA*
[1] Gravitational redshifts. Light rays from the stars must travel vast distances to reach us. It has
been proven that the pull of gravity, from the stars the light rays pass, could indeed cause a loss in
light-wave energy—thus moving that light toward the red on the spectrum. Einstein was the first
to predict that gravity would affect starlight, and this was shown to be true in the 1960s.—p. 35.
Albert Einstein was the first to predict that gravity would be able to affect the transmission of
light. This fact could easily explain the redshifts which have been found.—p. 42.
[2] Second-order Doppler shift. It is known that a light source moving at right angles to an
observer will be redshifted. Compare this fact with the known fact that all stars are definitely
circling galaxies. In addition, many scientists suspect that, just as all planets and stars are kept in
position by orbiting, so, for purposes of stability, the entire universe is probably circling a
common center!—pp. 35-36.
[3] Energy-loss shift. Light waves could themselves lose energy as they travel across the long
distances of space. This is called "tired light." The energy-loss shift is probably the primary cause
of the redshift.—p. 36.
http://www.angelfire.com/nt/fairytales/redshift.html
BLUE SHIFT
The blue shift is a decrease in the wavelength of the light that is emitted from an object that is
moving toward us. This decrease in wavelength makes the object appear to be bluer than it
actually is. For example, when a star is travelling towards Earth, its light appears bluer (the light
waves are shortened, shortening the wavelength). Compare with red shift.
http://www.allaboutspace.com/subjects/astronomy/glossary/indexb.shtml
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Activity: Determining Red-Shift in a Receding Star
Instructional Objectives
Time Needed for Activity
Target Grade Level
Materials
Background Information & Questions
Web Resources
Instructional Objectives:
Students will 1.
2.
3.
4.
manipulate multivariable algebraic formulas,
understand velocity, wavelength and frequency,
study the Doppler effect,
determine the amount of red-shift in light from a receding star.
Time Needed For Activity:
45 minutes
Target Grade Level:
Advanced high school students.
Materials:


Calculator
Dictionary
Background Information and Questions:
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careful his from stems discovery Hubble?s century. finding scientific significant most
many is was universe that>
Part 1: LIGHT WAVES
Light is best described as a wave. All waves are characterized by a wavelength and a
frequency.
The wavelength describes the distance between the crest of each cycle. The frequency is
the number of crests that pass any given point every second. Visible light waves range in
wavelength from approximately 400 nanometers
(400 nm = 400 x 10-9m) for violet colors to about 700 nanometers for red.
Correspondingly, violet has a frequency of about 7.5 x 1014 Hz (where 1 Hz is equal to 1
cycle/second) and red has a frequency of 4.3 x 1014 Hz.
Light is a type of electromagnetic radiation. Other types of electromagnetic radiation like
ultraviolet light, infrared light, radio waves and X-rays also travel in the form of a wave
but at wavelengths to which our eyes are insensitive.
Sound is not electromagnetic radiation, but sound is a wave as well. Higher pitches are
caused by higher frequencies of vibrating molecules that reach your eardrum. Lower
pitches are likewise caused by lower frequencies.
Questions:
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1. What color has the longest wavelengths?
2. What color has the shortest wavelengths?
3. What color has more crests of its wave passing a given point in one second?
Explain.
4. Look up the prefixes "ultra" and "infra" in the dictionary. Explain why the
wavelengths just out of the visible spectrum are referred to as ultraviolet and
infrared.
Part 2: DOPPLER EFFECT
If a wave source is moving, the crests of its waves get bunched together in front of the
wave source. If the wave crests are bunched together, their frequency increases. In the
case of a sound wave, the pitch is higher. Behind the wave source, the waves spread out
and the pitch is lower.
In the case of light we use the terms "blue-shift" and "red-shift" to describe how the
DOPPLER EFFECT changes the wavelength of the light. Being blue-shifted or redshifted doesn't mean that the light necessarily becomes blue or red. It means simply that
the light's wavelength either is shortened (blue shifted) because the object giving off the
light is approaching, or is lengthened (red-shifted) because the object is moving away
from the observer.
Part 3: DETERMINING THE COMPOSITION OF STARS
When energized atoms and molecules vibrate, they give off massless light particles called
photons. These photons travel as a wave, but because of quantum energy effects, a
particular type of atom or molecule gives off only certain wavelengths of photon light.
For example, when hydrogen atoms are giving off energy in the form of light, they emit
light specifically at wavelengths of 410.2 nm, 434.0 nm, 486.1 nm, and 656.3 nm. This is
called the emission spectra of hydrogen.
Scientists can use the emission spectra of atoms and molecules to study the composition
of stars. Scientists need simply to look very carefully at the intensity and wavelengths of
the light given off by the star. A star containing hydrogen, for example, would have
intense peaks of energy at 410.17 nm, 434.05 nm, 486.13 nm, and 656.28 nm. These
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hydrogen emission peaks would be in addition to the ones associated with the other
elements contained in the star.
Part 4: RECEDING STARS
In the 1920's, Edwin Hubble, while studying the stars of distant galaxies, found that for
some, their emission spectra had peaks at 411.54 nm, 435.50 nm, 487.75 nm, and 658.47
nm. Hubble knew that these wavelengths did not correspond to any known element and
that it was not likely that a combination of other elements or molecules was responsible.
He did notice that these spectral lines corresponded to hydrogen's emission spectra except
that they were all 0.0033 percent longer in wavelength than they should have been for a
hydrogen spectra. Hubble deduced that this red-shift must be because of a Doppler effect.
His calculations showed that these galaxies must be moving away from earth at 1 x 106
m/s (one million meters per second)!
Part 5: VERIFY HUBBLE'S WORK THAT SHOWS THE UNIVERSE IS
EXPANDING
For all waves, the product of wavelength and frequency gives the velocity of the wave
where (lambda) is the wavelength and f is the frequency.
v = (lambda) f
In the case of light and other electromagnetic radiation, however, the velocity is always
fixed at 3 x 108 m/s. This speed of light is assigned the variable c.
vlight = c = 3 x 108 m/s, or more precisely, c = 2.99792458 x 108 m/s
Use c = 2.9979 x 108 m/s for any calculations below. Also, use the appropriate number of
significant digits.
Questions:
1. What would the frequency be of a violet light wave with wavelength of 410.17
nm?
2. What frequency is associated with 434.05 nm?
3. What frequency is associated with 486.13 nm?
4. What frequency is associated with 656.28 nm?
5. Imagine the hydrogen atoms in one of Hubble's distant stars emitting a photon of
light at a wavelength of 410.17 nm. If that particular photon were headed directly
TOWARD Earth, how much CLOSER to us would that photon be after one
second? (Recall that the distance, d, that an object travels in a time, t is given by d
= vt where v is the object's velocity.)
6. Now if the star that emitted the photon were traveling AWAY from Earth at 1 x
106 m/s, how much FARTHER from Earth would the star be after one second?
7. After one second, what is the distance between our initial photon and its star?
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8. Our initial photon would be followed by many, many more just like it, each
behaving similarly to the first. After one second, how many wave cycles of
photons would stretch between the distant star and our initial photon?
9. What is the average wavelength of this photon light? (Hint: Use your answers
from 4 and 5 above.) Compare this with what Hubble saw.
10. Convince yourself of the validity of this process by repeating questions 2 through
6 for one more of the hydrogen emission spectra peaks at wavelengths 434.05 nm,
486.13 nm, or 656.28 nm. (Choose (a) the distance the photon travels toward
Earth, (b) the distance the star moves away from Earth, (c) the distance between
the photon and the star, (d) the number of cycles between the star and the photon,
(e) the effective red-shifted wavelength.)
11. If you were driving in a VERY fast car, how would the things you approach look
different from normal? How would the things you drive away from look
different? Explain.
12. Why do you think Hubble's discovery that the universe is expanding would have
been impossible without instruments that could precisely measure emission
spectra?
http://www.pbs.org/deepspace/classroom/activity2.html
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