This lesson introduces the observations of atomic spectra that motivated models of atomic structure. Spectral lines act like fingerprints: they reveal which elements are present, even in distant stars.
White light contains a continuous range of wavelengths. When it passes through a gas, atoms in the gas absorb light at particular wavelengths. A spectroscope then shows dark lines against the continuous spectrum; this is an absorption spectrum. The dark lines identify wavelengths removed from the light.
All flashcards
What is an absorption spectrum?
A pattern of dark lines at wavelengths absorbed by a gas, appearing against a continuous spectrum.
What is an emission spectrum?
A pattern of bright lines at wavelengths emitted by a gas, appearing against a dark background.
What are Fraunhofer lines?
Dark lines observed in the solar spectrum and accurately measured by Joseph von Fraunhofer.
Why does each element have a spectral fingerprint?
Each element absorbs and emits light at a characteristic set of wavelengths, producing a distinctive pattern of lines.
How can spectroscopy help astronomers?
By identifying characteristic spectral lines in starlight, astronomers can determine which elements are present in distant objects.
Quiz questions
What does an absorption spectrum look like?Answer: Dark lines at absorbed wavelengths against a continuous spectrum.
What does an emission spectrum show?Answer: The particular wavelengths of light emitted by a gas.
How are the absorption and emission lines of one element related?Answer: They occur at the same characteristic wavelengths.
How can astronomers use a star’s spectral lines to identify elements?Answer: They compare the line pattern with characteristic patterns produced by elements.
What did Cecilia Payne-Gaposchkin conclude from stellar spectra and ionization research?Answer: Stars are mostly hydrogen and helium, with hydrogen the most abundant.
Based on University Physics Volume 3 by Samuel J. Ling, Jeff Sanny, William Moebs (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.