PART 1: Calibration for Young's Experiment
Observe and record the identity and color of the gas in the glowing Geissler tube. These tubes contain gas at low pressure (about 0.001 atm). A high voltage electric discharge ionizes the gas, and the recapture of the electrons to characteristic energy levels results in a unique line spectrum. Place one meter stick parallel to the line of sight and another behind the tube as diagrammed below.
Using diffraction glasses, observe the line spectrum of helium. Twist your head until the colored lines are "standing" on the meter stick. Your partner should stand behind the meter stick and use a pencil to help you find the exact distance from the tube to each line above the meter stick (marked x in the diagram). Record this distance in centimeters.
Use Table 1 below to determine the wavelength of each line (as
an alternative, you may use the spectroscope with the internal wavelength
scale and read it directly). Use the known wavelengths to determine
the diffraction grating width (d) as follows:
The tube should be exactly 1.00 meters from your eyes. Use 100.0 cm as L. | L = 100.0 cm | |||||||||
The distance from the tube to the line is x. | Record x for each line | |||||||||
Calculate the distance from the diffraction grating to the line, using the Pythagorean Theorem. This distance is the hypotenuse (H). | L2 + x2 = H2 | |||||||||
The spacing of diffraction grooves, angle of diffraction, and wavelegth of the color line are related by the equation | l = dsinq | |||||||||
From trig, you may recall that |
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Substitute and solve for d: |
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Calculate an average value for d. | ||||||||||
Color | |
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purple | 388.9* | |
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blue | 447.2 | |
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blue | 471.3* | |
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blue/green | 492.2* | |
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green | 501.6 | |
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yellow | 587.6 | |
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red | 667.8 | |
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red | 706.5* | |
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Observe the line spectrum of hydrogen gas. Measure and record the distance of each line from the glowing tube. Use the equations from PART 1 to determine the wavelength of each line. From the wavelength, determine the associated frequency and energy for each electron transition in excited hydrogen.
Once you have determined the energy of each line in the hydrogen spectrum, use the Rydberg equation to determine from which energy levels the electrons "fall" (find ni; nf = 2).
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n |
E |
nf |
ni |
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(_____) |
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Helium Spectrum |
Constants & Relations |
Colors & Information |
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Be very careful about the signs: What is the sign for the frequency of light? What is the sign for the energy change of the electron? |
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Attach one sheet with orderly calculations for d (be very careful about the labels for d).
Attache one other sheet with orderly calculations for one of the values of
nf.