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Absorption and emission spectra
Beginner
Atoms emit and absorb light at specific wavelengths.
Hot gases emit light at discrete wavelengths (emission lines); cool gas in front of a continuous source absorbs the same wavelengths (dark lines). Each element has a unique pattern.
Fraunhofer lines in sunlight reveal the Sun's composition.
Helium was discovered in the Sun first.
In more detail
Atoms absorb light at the same wavelengths they emit, producing absorption and emission spectra. Each element has a unique set of lines, which can be used for identification.
Real-world uses
- Spectroscopy identifies elements in stars, gases and samples.
- Sodium lamps emit characteristic yellow light.
- Chemists identify elements in stars and lab samples by their unique emission and absorption spectra.
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Frequently asked questions
Why do dark lines appear in sunlight?
Atoms in the Sun's outer layers absorb light at specific wavelengths, creating dark Fraunhofer lines.
Can we tell which element emits a line?
Yes, each element has a characteristic pattern of lines.
Why do emission and absorption lines match?
An atom absorbs the same wavelengths it can emit, because the energy gaps between levels are the same in both processes.
Related topics in Atomic & Nuclear Physics
Energy of hydrogen levels · Hydrogen spectrum · Rydberg constant · Ionisation energy · Franck–Hertz experiment · Characteristic X-rays