Sunday, March 18, 2012
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Types of emission and absorption spectra:
1. Continuous emission spectrum: this spectrum consists of a wide range of unrepeated wavelengths (colours) in a definite wavelength range. The continuous emission spectrum is obtained by incandenscent solids (white hot solids), dense hot gases, liquid in bulk state. It does not depends on substance but depends on temperature of the substance only. The spectra obtained from luminous body like tungsten filament, burning coal, red hot metals, burning candles, stars and the sun are continuous emission spectra.
2. Line emission spectra: This spectrum consists of sharp lines of definite wavelengths (colours). The line emission spectra is produced by excited substance in atomic state as sodium vapour lamp, gases in discharge tube, mercury vapour lamp, luminous helium, argon, neon.
3. Band emission spectra: This spectrum consists of distinct bright bands of different wave lengths each having sharp edges. Incandescent vapours in molecular state. Calcium or barium salts in the Bunsen burner flame, nitrogen in molecular state in vacuum tubes give band emission spectra.
1. Continuous absorption spectra: it consists of absence of continuous wavelength range. When an unexcited substance is placed between the source and prism then continuous absorption spectrum is produced. That is when a blue glass is placed between the source of white line and prism, then all wavelengths excerpt blue and continuously absorbed.
2. Line absorption spectra: It consists of absence of sharp dark lines and is produced when an unexcited source of white light and prism that is, when a sodium vapour lamp is placed between the prism and tungsten filament, then two dark lines in yellow regions corresponding to wavelengths 5890 arm strong and 5896 arm strong are appeared in line absorption spectra due to absorption in chromospheres.
3. Band absorption spectra: It consists of absence of sharp dark bands and is produced when unexcited substance in molecular state is placed between the source and the prism.
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