![]() ![]() For example, when an electric discharge passes through a tube containing hydrogen gas at low pressure, the H 2 molecules are broken apart into separate H atoms and we see a blue-pink color. (credit: Dave Shaver)Įach emission line consists of a single wavelength of light, which implies that the light emitted by a gas consists of a set of discrete energies. This sign shows the elaborate artistic effects that can be achieved. Each element displays its own characteristic set of lines, as do molecules, although their spectra are generally much more complicated.įigure 8.2.1.Neon signs operate by exciting a gas at low partial pressure using an electrical current. Fluorescent light bulbs and neon signs operate in this way (Figure 8.2.1.). Exciting a gas at low partial pressure using an electrical current, or heating it, will produce line spectra. ![]() In contrast to continuous spectra, light can also occur as discrete or line spectra having very narrow line widths interspersed throughout the spectral regions such as those shown in Figure 8.2.2. ![]() These continuous spectra can often be approximated by blackbody radiation curves at some appropriate temperature, such as those shown in Figure 8.1.9 in the previous section. Incandescent (glowing) solids such as tungsten filaments in incandescent lights also give off light that contains all wavelengths of visible light. As can be seen in Figure 8.1.8 in the previous topic, sunlight also contains UV light (shorter wavelengths) and IR light (longer wavelengths) that can be detected using instruments but that are invisible to the human eye. You can see all the visible wavelengths of light present in sunlight by using a prism to separate them. Most of the light generated from stars (including our sun) is produced in this fashion. Photons produced in this manner have a range of energies, and thereby produce a continuous spectrum in which an unbroken series of wavelengths is present. When solids, liquids, or condensed gases are heated sufficiently, they radiate some of the excess energy as light. Another paradox within the classical electromagnetic theory that scientists in the late nineteenth century struggled with concerned the light emitted from atoms and molecules. ![]()
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