Physics Home > Teaching Labs > Modern Physics > Hydrogen Spectrum

Topics

Points of Emphasis

Prerequisites

Lab Activities

Measurement of the alpha, beta, and gamma emission lines of hydrogen with an optical spectrometer. Using those wavelengths, the energy of the photons producing those lines are computed and compared to the photon energies as predicted by the Bohr theory for the hydrogen atom. Results tend to be within 1% of the accepted values.

There is also a version of the lab which replaces the optical spectrometer with a diffraction grating-meter stick system. The students line up the emission line of interest with a pointer on the diffraction grating and with a movable pointer on the meter stick; and from the position of the pointer on the meter stick, the distance from the meter stick to the diffraction grating and the number of lines per cm of the diffraction grating, compute the wavelength of the emission line. Although the measurement system is crude, the quantitative results are within 1-2% of the accepted values and there is the advantage that it shows very clearly how a simple spectrometer works.

Course Level

Introductory

Student Handouts

Equipment

Number of set-ups available: 5 Per lab station: 1 spectrometer/diffraction grating 1 hydrogen spectrum tube 1 spectrum tube power supply 1 flashlight 1 Handbook of Chemistry and Physics 1 cross hair illuminator 1 small lamp 1 spectrometer stand 1 eye patch 1 box of spectrum tubes for other gases

Notes

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