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Title:  Atomic Spectrum of Hydrogen

Purpose: To determine the wavelengths of light emitted from excited hydrogen atoms.



1.  Do not put your fingers near either of the electrodes of the power supply when it is on.

2.  Do not look for an extended period of time at the gas tubes when lit, the UV light is damaging to your eyes.

3.  Do not allow the gas tubes to be on for long periods of time: the tube will be damaged and you will obtain faulty readings of the gas's spectral lines.

Perform the following steps using both a H2 and a Hg gas tube.  The order is unimportant, but readings for both tubes must be complete.

1. Stand the power supply vertically and insert the gas tube into the appropriate fittings.  Ensure the power supply is plugged in.

2. Place a spectroscope on a steady platform (you may use books) such that the vertical slit of the spectroscope is at about the same height as the center of the gas tube and the numbers inside the spectroscope are right side up.

3. Turn on the power supply and line up the spectroscope to obtain spectral lines of maximum brightness (there should be about 3-4 visible lines).  Record the position where  these spectral lines fall on the spectroscope scale to the nearest 0.05 units.

4. Shut off the power supply.  Repeat steps 1-4 for the other gas tube.


1. The visible spectral lines of Hg have the following values: violet, 404.7 nm; blue, 435.8 nm; green, 546.1 nm; yellow, 579.0 nm.  Using the data you recorded, make a calibration curve plotting the above wavelengths in nm vs. your corresponding spectroscope readings on the x-axis.  Be sure to label all axis and title your graph.  Your graph should be at least ½ page big.  Draw a best fit straight line through your data points.

2. Using your calibration curve determine the wavelength of the observed H2 spectral lines.  From your book, find the accepted values for the observed spectral lines of H2 and calculate the % error for each of your reported wavelengths.

3. Determine the corresponding energy of the accepted wavelengths of H2's spectral lines using E = hv .

4. Using Bohr's equation for a hydrogen atom, determine which transitions (e.g. from n = 4 to n = 1 ?) in the hydrogen atom are responsible for the wavelengths of light you observed in this lab.