Microsoft Word - Exp 12 Lasers and Spectra.doc
���� Experiment 12
Lasers and Spectral Emissions of Light
�
� The concept that electrons occupy only quantized energy levels has revolutionized
our understanding of matter. The energy of light can be determined from its wavelength
"lambda" (expressed in nm, 109nm = 1 m) and the speed of light "c" XXXXXXXXXXx 108 m/sec)
and Planck's constant "h" XXXXXXXXXXx 10-34 J sec) using:
E = hc/�
The wavelength of light is associated with the color we see according to the following
chart.
Wavelength (nm or 10-9m) Color
XXXXXXXXXXred
XXXXXXXXXXyellow
XXXXXXXXXXgreen
XXXXXXXXXXblue
XXXXXXXXXXviolet
XXXXXXXXXXUltra Violet (invisible)
Part A Element Lamps
Materials: Hydrogen, argon, neon, mercury, helium and sodium (if possible) emission
lamps with spectroscopes
Hypothesis: Do elements emit line spectra? Can we identify an element from its line
spectra?
Observe the hydrogen lamp through the spectroscope. Record the color and
wavelength of the
ight, prominent lines (3 significant figures). Faint, closely spaced
lines are emitted by molecular hydrogen and should not be recorded. You should be
able to see at least three lines. Calculate the energy (show your work) using the
equation above for each of the 3 observed lines.
Make the same observations for the argon bulb, recording wavelength and color of the
five
ightest lines.
Other Lamps: There are 3 other lamps, labeled A, B, and C. Look at the other lamps
present and identify the element based on comparison with the chart on the back of
your lab book. Each element exhibits its own characteristic absorption line spectrum
due to differences in the energy levels of the electrons. When elements are heated in a
flame, electrons are promoted to excited states with energy higher than the normal
ground state. We can identify many elements based on the characteristic color that is
produced when the electrons drop from their excited state to a lower state and emit
light.
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Part B Lasers
Materials: laser, holograms, fiber optics, chalk dust or laser spray, diffraction grating
Hypothesis: Do holograms project 3D images? What are some ways lasers can be
used?
In the last part of this experiment we will explore some applications of quantum theory
used in the real world. We will focus on the laser. The acronym LASER stands for Light
Amplified by Stimulated Emission Radiation. A laser consists of a tube containing a
lasing medium with two mi
ors on each end. See below.
The medium is energized using an electric cu
ent, a flash lamp, or even a chemical
eaction. The atoms or molecules are energized to their excited state. On the molecular
time scale, the molecules slowly return to their ground state. As they do so they emit light
energy in all directions. However, a few will by chance emit light energy along the axis of
the tube toward one of the mi
ors on the ends of the tube. As it does so it runs into other
excited molecules. These collisions induce the excited molecules to prematurely return to
their ground state emitting light energy along the axis of the tube in step with the original
colliding light wave. As these light waves travel up and down the tube reflecting off the
mi
ors at each pass, they pick up many other light waves by stimulating the emission
through collisions. Thus the LIGHT is AMPLIFIED by STIMULATING EMISSION forming
RADIATION of light (LASER). One mi
or on one end is only partially reflecting. When
the light intensity exceeds a certain point the light shoots right through out the end of the
laser. The result is a straight monochromatic (all of the same color or wavelength)
coherent (all waves matching up or in step) light we call laser light.
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Part C Optical Mirage
When two parabolic mi
ors are placed on top of each other as shown below, an object
placed in the center of the bottom mi
or will reflect off of the top mi
or, then down to the
ottom mi
or and produce a virtual image above a hole in the top mi
or. This virtual
image will appear real but as you go to touch it, nothing is there! Try to grab the pink pig.
Draw in the pig on the report sheet where it really is and where it appears to be with the
eal pig circled.
Part D Night Quest Experiment
Each student or pair of students will sign out a Night Vision card containing a diffraction
grating and line spectra of various night time lights. You are to take this home and at
night look at various lights through the diffraction grating hole. You are to identify 4
different kinds of lights by comparing the line spectra you observe through the diffraction
grating with the line spectra printed on the card. You should record the location (detail)
and the type of light on your lab report.
Part E Stoke’s Shift Experiment
When an atom abso
s energy at a
higher energy and then re-emits at a
lower energy, it is called the Stoke’s Shift.
The emitted energy is always lower than
the abso
ed energy. The change in
energy is due to the loss of energy due to
vi
ations. Calculate this loss by using
E=hc/� for UV light minus green light of
the fluorescent Vaseline glass. Do the
same for the blue light of the Canada Dry
Tonic water. Do the same for the yellow
light abso
ed by the light bulb and the
ed fluorescent light of the yellow and green food colors in alcohol.
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Experiment 12-Lasers Emissions Lab Report
Name: __________________________________ Section: _________________
Part A Element Lamps
Element Lamp Color of Line Wavelength Energy Calculations (Hydrogen only)
Hydrogen
Argon
Element A ______________________
Element B ______________________
Element C ______________________
Part B Lasers
Lasing medium: _______________ XXXXXXXXXXhologram images: _______________
XXXXXXXXXXLaser color: _______________ XXXXXXXXXXexcitation method: _______________
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Part C Optical Mirage
Part D Night Quest
XXXXXXXXXXType of Light from Card
Location XXXXXXXXXXNo Duplicates)
1. ___________________________________ _____________________
2. ___________________________________ _____________________
3. ___________________________________ _____________________
Part E Stoke’s Shift Calculation (Show your work)
Energy of UV light =
Energy of Green light =
Energy of Blue light =
Energy of Yellow Light =
Energy of Red Light
Energy of UV light – Energy of Green light =
Energy of UV light – Energy of Blue light =
Energy of Yellow light – Energy of Red light =
Phys Science 12 Experiment 12 Line Spectra = 700
E=hc/λ = (6.621x10-34Js)(2.9979x108m/s)/(7.00x10-7m)
For λ = 700nm (red)
E should be something x10-19J (be sure to enter unit of J)
Argon Line Spectrum
Lamp A
Lamp B
Lamp C