Research Papers in Physics and Astronomy
Title
Physics, Chapter 42: Optical Spectra and Atomic Structure
Document Type
Article
Date of this Version
January 1958
When light passes through a prism spectroscope or a diffraction-grating
spectroscope, an optical spectrum is obtained in which the intensity of
the radiation may be analyzed as a function of wavelength. The spectrum
may be observed visually in the limited wavelength region to which the
eye is sensitive; it may be focused on a photographic plate or upon a
thermocouple or thermopile. Our knowledge of the structure of atoms
and molecules is largely dependent upon the analyses of optical spectra,
for these spectra are characteristic of the emitting atoms or molecules.
Even before the spectra of atoms were properly understood in terms of
the atomic structure, it was possible to determine the chemical composition
of an unknown substance by study of its spectrum.
The spectra obtained from radiating bodies are called emission spectra
and are classified as continuous spectra, band spectra, and line spectra,
according to their appearance in a spectroscope. Continuous spectra are
emitted by solids, liquids, and dense opaque gases at high temperatures.
The spectrum of the sun, or of a black body, is a continuous spectrum and,
as we have seen in Section 18-6, the shape of the black-body spectrum is
characteristic of its temperature. Gases at low pressures emit band or line
spectra. Line spectra have their origin in the energy changes which take
place in the atoms of a gas, while band spectra are associated with similar
changes in the molecules.
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Published in Physics, by Henry Semat and Robert Katz, New York: Rinehart & Company, Inc., 1958. Copyright © 1958 Henry Semat and Robert Katz. All rights reserved. Used by permission.