The band absorption spectra are used for making dyes. If white light is allowed to pass through iodine vapour or dilute solution of blood or chlorophyll or through certain solutions of organic and inorganic compounds, dark bands on continuous bright background are obtained. When light from the carbon arc is made to pass through sodium vapour and then examined by a spectrometer, a continuous spectrum of carbon arc with two dark lines in the yellow region is obtained as shown in Fig.5.5. It is the characteristic of the absorbing substance.Ībsorption spectra is also of three typesĪ pure green glass plate when placed in the path of white light, absorbs everything except green and gives continuous absorption spectrum. When the light emitted from a source is made to pass through an absorbing material and then examined with a spectrometer, the obtained spectrum is called absorption spectrum. Using band spectra the molecular structure of the substance can be studied. When the bands are examined with high resolving power spectrometer, each band is found to be made of a large number of fine lines, very close to each other at the sharp edge but spaced out at the other end. Calcium or Barium salts in a bunsen flame and gases like carbon - di - oxide, ammonia and nitrogen in molecular state in the discharge tube give band spectra. It is the characteristic of the molecule. It consists of a number of bright bands with a sharp edge at one end but fading out at the other end.īand spectra are obtained from molecules. The substance in atomic state such as sodium in sodium vapour lamp, mercury in mercury vapour lamp and gases in discharge tube give line spectra (Fig. It is used to identify the gas.Ītoms in the gaseous state, i.e. It is the characteristic of the emitting substance. Line spectra are sharp lines of definite wavelengths. Incandescent solids, liquids, Carbon arc, electric filament lamps etc, give continuous spectra. These spectra depend only on the temperature of the source and is independent of the characteristic of the source. It consists of unbroken luminous bands of all wavelengths containing all the colours from violet to red. Every source has its own characteristic emission spectrum. When the light emitted directly from a source is examined with a spectrometer, the emission spectrum is obtained. The spectra obtained from different bodies can be classified into two types (i) emission spectra and (ii) absorption spectra. These images are the emission lines of sodium having wave lengths 5896A o and 5890A o. If the slit is illuminated with light from sodium vapour lamp, two images of the slit are obtained in the yellow region of the spectrum. The image obtained in the field of view of the telescope consists of a number of coloured images of the slit. When white light falls on a prism, placed in a spectrometer, the waves of different wavelengths are deviated to different directions by the prism.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |