Download Spectral lines, wavelength of light, Rydberg constant

ATSC 5003 Atmospheric Radiation Lab
Spectral lines, Wavelength of light, Rydberg Constant
Spectral lines general
1) With either a diffraction grating or a hand held spectrometer, observe the spectra of the following
gases: argon, helium, hydrogen, mercury, neon, sodium. Identify them, by writing the tube
number next to each gas, and a short description of the lines. Record these on table attached.
Element
Argon
Helium
Hydrogen
Mercury
Neon
Sodium
Tube#
Description
2) With hand held spectrometer describe the differences between the spectra of incandescent light
and fluorescent light. The spectrum of which gas is observable in the fluorescent light. Use this
gas to calibrate the spectrometer using the green line at 546 nm.
3) With hand held spectrometer observe the spectra of a bright spot, cloud, in the direction of the
sun, and then a white piece of paper on the ground. How do they compare? Identify the
wavelengths of at least two missing (absorption) lines. What causes these lines?
Measuring the wavelength of light.
1) Tabletop spectrometer set up: With an incandescent light through a pinhole, and diffraction
grating aligned perpendicular to the beam of light, align the base table of the spectrometer so that
when the order 0 slit (all colors) is in the cross hairs, the angle is reading 0. This can be done by
adjusting the position of the round table. You may also wish to level the diffraction grating to
align the vertical cross hairs with the slit (optional). Record the line spacing for the diffraction
grating used. Keep the same diffraction grating for all measurements.
2) With the incandescent light source find the first order maximum. Record the angles (nearest arc
minute) for the visible wavelength range (red to violet). Do the same for the first order maximum
in the opposite direction. How do the two first order maxima compare? Can you find the second
order maximum? How does it compare with the first order? Calculate the wavelength range of
visible light for your measurements.
3) Replace the incandescent source with either a helium or mercury source. Record the deviation
angle, to the nearest arc minute, for the two brightest lines in the spectra. Repeat this
measurement for the symmetric first order pattern on the opposite side. Record the average
deviation angle for each line and calculate the wavelength. Compare these wavelengths with
those found in table A8. This comparison will help calibrate the spectrometer for use in
determining the Rydberg constant. Measure the wavelength of the next three brightest lines in the
spectra and compare with the table.
Color
second order
Incandescent
light
Red edge
Violet edge
Mercury or
Helium
Brightest
Brightest
Next 3a
Next 3b
Next 3c
Deviation Deviation Average
angle 1,
angle in
deviation
first order opposite
angle
direction,
first order
Wavelength Deviation
Wavelength
angle, Second
order, may be
difficult to
find.
Rydberg constant. Recall Rydberg's formula, 1/ = k = R (1/22 - 1/n2) for Hydrogen
1) With the calibrated spectrometer. Measure the deviation angle and calculate the wavelength (m)
of the first 4 lines of the Balmer series for hydrogen, beginning in the red (n=3). For each line,
record: color, deviation angle, n. Calculate , k, 1/n2. Prepare a table of these values. Be sure that
the wavelengths recorded here are those you obtain after accounting for the calibration of your
spectrometer.
2) Plot k versus 1/n2. How well do the data match expectations? Describe differences. Calculate the
Rydberg constant from at least two sets of your measurements. Estimate the errors on your
estimate. Compare your values with the true value. Are your measurements in agreement with
theory within experimental uncertainties.
3) Why are only 4 lines visible in the Balmer series. Lines do exist for n > 6. What wavelength
represents the n= line?
Color
Deviation angle
Rydberg constant
Wavelength
k = 1/
1/n2
n
3
4
5
6
