What is Absorption spectrum? — Physics

Definition 2.14 High School Physics · Chapter 2 — Light Spectra and the Message of Light

Send white light through a cool, low-pressure gas and disperse what comes out: the continuous rainbow reappears, but scored by thin dark lines. The gas has removed certain wavelengths from the passing light. Such a spectrum — a continuous background minus a set of lines — is an absorption spectrum.

The two spectra of hydrogen: bright emission lines (top) and dark absorption lines (bottom) at exactly the same wavelengths, 410, 434, 486 and 656\, nm. — The two spectra of hydrogen: bright emission lines (top) and dark absorption lines (bottom) at exactly the same wavelengths, $410$ , $434$ , $486$ and $656\,\mathrm{nm}$ .

Examples

Example 2.17 (A flask of sodium vapor)

White light crosses a flask containing cool sodium vapor. The transmitted spectrum is a full rainbow with one dark line at $589\,\mathrm{nm}$ — precisely where a sodium lamp shines brightest. Looking at the flask from the side in a dark room, one sees the stolen light re-emitted: a faint yellow-orange gleam at that same wavelength.

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Examples

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