单词	spectrum
释义	spectrum 1 A distribution of entities or properties arrayed in order of increasing or decreasing magnitude. For example, a beam of ions passed through a mass spectrograph, in which they are deflected according to their charge-to-mass ratios, will have a range of masses called a mass spectrum . A sound spectrum is the distribution of energy over a range of frequencies of a particular source. 2 A range of electromagnetic energies arrayed in order of increasing or decreasing wavelength or frequency (see electromagnetic spectrum). The emission spectrum of a body or substance is the characteristic range of radiations it emits when it is heated, bombarded by electrons or ions, or absorbs photons. The absorption spectrum of a substance is produced by examining, through the substance and through a spectroscope, a continuous spectrum of radiation. The energies removed from the continous spectrum by the absorbing medium show up as black lines or bands. With a substance capable of emitting a spectrum, these are in exactly the same positions in the spectrum as some of the lines and bands in the emission spectrum. Emission and absorption spectra may show a continuous spectrum , a line spectrum , or a band spectrum . A continuous spectrum contains an unbroken sequence of frequencies over a relatively wide range; it is produced by incandescent solids, liquids, and compressed gases. Line spectra are discontinuous lines produced by excited atoms and ions as they fall back to a lower energy level. Band spectra (closely grouped bands of lines) are characteristic of molecular gases or chemical compounds. See also spectroscopy. Spectrum: sources of electromagnetic spectra
随便看	troposphere tuned circuit tuning fork tunnel diode tunnel effect turbine turbogenerator turbojet turbulence turns ratio tweeter twin paradox Tyndall effect ultracentrifuge ultrahigh frequency ultramicroscope ultrasonic imaging ultrasonics ultraviolet microscope ultraviolet radiation umbra uncertainty principle underdamped uniaxial crystal unified-field theory

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