# Spectrum (physics)

In physics, a spectrum is the distribution function of a physical quantity - for example energy, frequency or mass. Depending on the size considered, the quantity, frequency, rate, flow or intensity of the respective size value is determined as the quantity measure. To put it simply, the spectrum contains the information about "how much" of which quantity of the physical quantity is available, ie about "how much" of the light under consideration has frequencies of the red, yellow, blue ... spectral range. Emission spectrum (specific radiation depending on the wavelength) of a blackbody for temperatures from 100 K to 10000 K in a double logarithmic coordinate system. There is a continuous spectrum here.

Important spectra are

1. the electromagnetic spectrum , in which the illuminance is considered as a function of the radiation frequency,
2. the energy spectrum, in which the rate or number of particles is considered as a function of their energy (e.g. electron spectrum ),
3. the acoustic spectrum, in which the sound intensity is considered as a function of the frequency of the sound (see sound spectrum , sound spectrum ),
4. the mass spectrum, in which the frequency of particles is viewed as a function of their mass (see mass spectroscopy ).

An emission spectrum characterizes a source. An absorption spectrum describes the change in an emission spectrum caused by a sample. The sensitivity of a sensor can also be displayed as a spectrum depending on the size to be measured.

Spectra can be the result of a measurement or can be calculated using theoretically sound model assumptions.

In a purely continuous spectrum , the observed variable also assumes all real intermediate values in a range , so the quantity measure is a continuous function of the variable. This is to be distinguished from a discrete spectrum ( line spectrum ), which only shows values ​​different from zero at separate ( discrete ) points or, conversely, is only zero at discrete points. The latter case is also called a discontinuous spectrum . In real discrete spectra ( line spectra ) the lines are broadened by convolution . There are also mixed forms as a superposition of both types.

Continuous spectra can be observed , for example, with thermal radiation and synchrotron radiation . Individual atoms emit electromagnetic radiation with a discrete spectrum.

Commons : Spectrum  - collection of images, videos and audio files
Wiktionary: spectrum  - explanations of meanings, word origins, synonyms, translations

## Individual evidence

1. a b c d spectrum. In: Lexicon of Physics, Spektrum Verlag Heidelberg. 1998, accessed March 14, 2017 .
2. ^ Dieter Meschede : Gerthsen Physics . 24th revised edition. Springer, Heidelberg 2010, ISBN 978-3-642-12893-6 , pp. 504-505 .
3. ^ Donald H. Perkins : Introduction to High Energy Physics . 3. Edition. Addison-Wesley, 1986, ISBN 0-201-12105-0 , 5.13 Heavy-Meson Spectroscopy and the Quark Model, pp. 170 , Fig. 5.10 (English).
4. ^ Dieter Meschede : Gerthsen Physics . 24th revised edition. Springer, Heidelberg 2010, ISBN 978-3-642-12893-6 , 4.6 Sound waves, pp. 189-197 .
5. ^ Donald H. Perkins : Introduction to High Energy Physics . 3. Edition. Addison-Wesley, 1986, ISBN 0-201-12105-0 , 4.6 Dalitz Plots, pp. 123 , Fig. 4.8. (English): "(...) The effective mass spectrum Λπ + is shown at right."
6. Jürgen Falbe, Manfred Regitz: Römpp Lexikon Chemie, 10th edition, 1996-1999: Volume 2: Cm - G . Thieme, May 14, 2014, ISBN 978-3-13-199971-9 , p. 1147.
7. absorption spectrum. In: Lexicon of Biology, Spektrum Verlag Heidelberg. 1999, accessed March 25, 2017 .
8. For example with the prism spectrometer: Hermann Döhler: Gaining information through measurement: Basics and applications of signal analysis . expert verlag, 2006, ISBN 978-3-8169-2568-2 , pp. 472f.
9. JJ Balmer: Note on the spectral lines of hydrogen , Annalen der Physik Vol. 25 (1885) pp. 80-87 (online at wiley: Vol. 261 Issue 5).