![]() ![]() Such emission spectra were observed for many other elements in the late 19th century, which presented a major challenge because classical physics was unable to explain them. (b) When the light emitted by a sample of excited hydrogen atoms is split into its component wavelengths by a prism, four characteristic violet, blue, green, and red emission lines can be observed, the most intense of which is at 656 nm. (a) A sample of excited hydrogen atoms emits a characteristic red light. With sodium, however, we observe a yellow color because the most intense lines in its spectrum are in the yellow portion of the spectrum, at about 589 nm.įigure 6.9 The Emission of Light by Hydrogen Atoms The light emitted by hydrogen atoms is red because, of its four characteristic lines, the most intense line in its spectrum is in the red portion of the visible spectrum, at 656 nm. When the emitted light is passed through a prism, only a few narrow lines, called a line spectrum A spectrum in which light of only a certain wavelength is emitted or absorbed, rather than a continuous range of wavelengths., are seen ( Figure 6.9 "The Emission of Light by Hydrogen Atoms"), rather than a continuous range of colors. Unlike blackbody radiation, the color of the light emitted by the hydrogen atoms does not depend greatly on the temperature of the gas in the tube. ![]() For example, when a high-voltage electrical discharge is passed through a sample of hydrogen gas at low pressure, the resulting individual isolated hydrogen atoms caused by the dissociation of H 2 emit a red light. ![]() zip file containing this book to use offline, simply click here.Īlthough objects at high temperature emit a continuous spectrum of electromagnetic radiation ( Figure 6.6 "Relationship between the Temperature of an Object and the Spectrum of Blackbody Radiation It Emits"), a different kind of spectrum is observed when pure samples of individual elements are heated. You can browse or download additional books there. More information is available on this project's attribution page.įor more information on the source of this book, or why it is available for free, please see the project's home page. Additionally, per the publisher's request, their name has been removed in some passages. However, the publisher has asked for the customary Creative Commons attribution to the original publisher, authors, title, and book URI to be removed. Normally, the author and publisher would be credited here. This content was accessible as of December 29, 2012, and it was downloaded then by Andy Schmitz in an effort to preserve the availability of this book. See the license for more details, but that basically means you can share this book as long as you credit the author (but see below), don't make money from it, and do make it available to everyone else under the same terms. Therefore, when this light passes through a gas, the gas atoms may absorb certain wavelengths to produce a line absorption spectrum.īlack hydrogen absorption lines are at the same wavelength as the bright hydrogen emission lines.This book is licensed under a Creative Commons by-nc-sa 3.0 license. This is called a line absorption spectrum. So if a continuous spectrum travels through a cooler gas, it will ‘pull out’ or absorb certain wavelengths of light to produce a series of dark lines on a continuous spectrum of light. When a gas is cool, it absorbs the same wavelengths of light as it would emit when it is hot. A gas cloud on its own, without a light source behind it, produces a line emission spectrum. Hot gases don’t produce a continuous emission spectrum.Ī hot gas only emits certain wavelengths of light to produce bright lines on a dark background. When a gas is very hot, it doesn’t emit all wavelengths of light. A light source, such as a star or a filament bulb, gives a continuous emission spectrum. This is called a continuous emission spectrum. This light, when seen through a prism or diffraction grating, shows all wavelengths of visible light. Studying the line spectra produced by hot gases and absorbed by cooler gases allows us to identify the elements in stars. ![]()
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