2014-15 REPLACEMENT for p.68-70, Lab F, Atomic Spectra
B. Observing Everyday Spectra
We will start by using spectroscopes to examine the spectra of light coming from an
incandescent bulb, a fluorescent light and light passing through Windex. Everyone
must make each observation, and then record the group consensus below.
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Draw the spectrum in two ways. First, as it appears visually, using appropriate
colors and intensities and positions with respect to the wavelength calibration
numbers. Second, draw a representation of the spectrum as a graph of intensity
as a function of wavelength, as shown in the introduction. Do these carefully.
Light Source
Naked
Eye
Color
Type of
Color / Wavelength (Nanometers)
Spectrum
Deep Red
Orange-Yellow
700
(650)
600
(550)
Green-Blue
Violet
500
400
(450)
Fluorescent
Light Bulb
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Incandescent
Light Bulb
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Windex
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(see
instructions
next page)
Replacement (a-e), p. a
2014-15 REPLACEMENT for p.68-70, Lab F, Atomic Spectra
For the Windex, observe the solution with a light bulb illuminating it from behind, and
move back and forth quickly to observe the light bulb without going through the Windex.
This will help you see the differences.
1. What part of the continuous spectrum from the lightbulb has been absorbed by the
Windex?
C. Observing Emission Spectra from hot gas
There are seven gas discharge tubes set up around the lab. Your group will visit each of
them as they are available, and use the spectroscopes to visually inspect, and then the
iPads to measure their spectra. The goal is to identify which element is in each
discharge tube by comparing their spectra with the spectral catalog provided by the TA.
There is a Spectrum Analysis poster in your lab room. Refer to it when you get
confused!
OVERALL QUESTIONS: Think about the following questions as you examine the
tubes, and answer them after you have examined each of the tubes.
1. Each tube contains a different gas. Are any of the spectra identical to each other?
Why or why not?
2. What features, other than the specific colors present, are different among the gases?
3. Based on your new knowledge of spectra, which of the following gases cannot be
present in the fluorescent light bulb? Neon, Hydrogen or Mercury
4. The gas at the surface of the Sun is cooler at the top, and then hotter as you go
towards the center. What type of spectrum would you expect to see from sunlight?
If it is sunny outside, point your spectroscope out the window and look at a bright
reflection of the Sun, to confirm your answer. Do NOT look directly at the Sun.
Replacement (a-e), p. b
2014-15 REPLACEMENT for p.68-70, Lab F, Atomic Spectra
MEASURING SPECTRA:
1. Get an iPad from your TA, specially equipped with a diffraction grating (spectroscope)
over the camera.
You are responsible for the safe return of this iPad at the end of the lab.
2. Launch the AstroSpec app on the iPad.
3. Go to one of the gas discharge lamps and turn it on.
4. On the ‘Dashboard’ tab, press the ‘File...’ button, and select ‘Take Photo’.
5. Hold the camera 6”-12” away from the lamp and slowly rotate the lens/grating on the
back until the line in the spectrum are vertical on the screen, as shown below. There
may be multiple spectra visible; choose the brightest and take a picture using the white
shutter button on the right.
6. If the lines look bright and clear, press ‘Use Photo’; otherwise press ‘Retake’.
7. We are now going to create the graph of the spectrum. To do this, start by cropping
the image to just include the spectrum. On the photo, draw with your finger a box about
1cm tall across just the spectral lines. Avoid including the lamp itself or any other
contaminating light elements.
BLUE
RED
Click ‘Crop’ to crop the image. Click ‘Spectrum’ to make the graph. (Choose
‘Restore’ to start over if needed.)
8. Select the lamp number (written on the side of each lamp) from the drop-down box.
9. Press ‘Save.’ If this lamp number has already been recorded, you will be prompted
to ‘Overwrite’ the current saved image. The spectra will be saved to the ‘Images’ tab.
10. Turn off the gas discharge lamp.
11. Show your first spectrum to your TA. Repeat from step 3 for each lamp.
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2014-15 REPLACEMENT for p.68-70, Lab F, Atomic Spectra
EXAMINING THE SPECTRA and CLASSIFYING
11. From the ‘Images’ tab, press any of the saved images to launch the gallery. Swipe
left and right to view the spectra you made for each lamp. Press the ‘x’ in the top right
to close the gallery.
12. Compare your graphs to those on the Gas Emission Spectrum sheet to fill out the
following chart.
13. At the end of lab, after the TA has reviewed all the identifications, erase all of your
photos by pressing ‘Clear all’ in the ‘Images’ tab. You will be prompted to ‘Confirm.’
14. Power off the iPad by holding down the power switch on the top-right of the iPad
(left side if held in portrait mode). ‘Slide to power off’ on the top of the screen.
Return the iPad and the lens, with its cap, to your TA.
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2014-15 REPLACEMENT for p.68-70, Lab F, Atomic Spectra
ELEMENT IDENTIFICATION CHART
LAMP #
Colors of Bright Lines
Other distinguishing
features
Proposed
Identification
1
2
3
4
5
6
7
PRINT NAMES
__________________ __________________ _______________ _______________
SIGNATURES
__________________ __________________ _______________ _______________
Replacement (a-e), p. e