Band Emission Spectra (R2) [7B10.10]
Spectra
Gas discharge lamps filled with different gasses such as hydrogen, helium, mercury,neon, and argon can be looked at through a piece of replica transmission grating or a thin slit on an index card. Their corresponding line spectra can be observed. A regular incandescent lamp with or without a red filter placed in front of it can also be looked at through a thin slit.
1. Spectrum Tube Power Supply
2. Various gas-filled tubes (e.g. Hydrogen, Helium, Argon, Krypton, Mercury)
3. Hand-held diffraction gratings
Row X
Procedure:
Place a gas-filled tube in the power supply, dim or turn off the lights, and turn on the power supply. Hold the diffraction grating up to your eye and observe the spectrum of the gas.
Explanation:
When a voltage is applied across the gas tubes, electrons in the gas are excited to higher energy levels. The electrons eventually return to their ground states, emitting light in the process. Because of the rules of electron transitions, atoms only emit specific frequencies of light. The diffraction gratings spread the incoming light into a spectrum, where one can see emission features at these specific frequencies. Thus, one can identify a gas by its emission spectrum.
Tags: diffraction, spectra
