(OPTICS) A plot of the intensity
of electromagnetic radiation radiation
at different wavelengths; in the
case of visible light, this is the familiar rainbow
of colors. An object that emits radiation in a continuous range of colors
is said to have a continuous spectrum.
An object that emits radiation only at certain wavelengths is said to
have emission lines; objects that absorb
radiation only at certain wavelengths are said to have absorption
lines. A good spectrum of a star, for example, reveals, among other
things, its spectral type, radial
velocity, and metallicity.
|There are two fundamental types of line spectra:
an emission spectrum and an absorption spectrum. An emission (A)
spectrum (A) is the result of exciting a substance so that its
electrons move to a higher energy. Photons are given out when
the electrons fall back to their original state. Conversely, an
absorption spectrum (B) is obtained when a photon is absorbed,
raising the electrons of an atom to a higher level. A substance
that emits light at a certain frequency absorbs light at the same
frequency. When white light passes through a substance (C), an
absorption spectrum can be seen – that is, the full spectrum
(except for black lines) at the wavelengths the substance would
emit if glowing alone.
- (QUAN. MECH.) The set of allowed
energy levels of a particle or
system. It is directly related to bright or dark lines in a spectrum
of light produced by a prism.
- (MATH) The set of eigenvalues
of a linear transformation. By historical coincidence, it is equivalent
to the notion of a spectrum in quantum mechanics.