Wednesday, May 11, 2011

Spectrum

When a beam of polychromatic light is passed through a prism, it is broken up into its constituent colors. This array of colors is known as Spectrum.
There are two principle classes of spectrum;

(a). EMISSION SPECTRUM
When the radiations emitted from the source are passed directly through the prism, the spectrum so obtained is known as Emission Spectra. (The source can be made to emit the radiations by heating the source to high temperature or by passing electric discharge).
Emission Spectrum is further classified into Continuous Emission Spectrum and Line Emission Spectrum.
i) Continuous Emission Spectrum:-
When the different colors of the spectrum overlap each other, a band of colors is obtained. Such a band of colors is known as Continuous Spectrum. Thus, the continuous spectrum obtained during the study of emission spectrum is known as Continuous Emission Spectrum. This type of spectrum is obtained whenever matter in bulk is heated.
ii) Line Emission Spectrum:-
When the different colors of the spectrum are separated from each other by dark spaces, the spectrum so obtained is known as Line Spectrum. Thus, the Line Spectrum obtained during the study of emission spectrum is known as Line Emission Spectrum. This type of spectrum is obtained whenever matter in atomic state is heated. Each line in spectrum corresponds to a particular wavelength. It has been observed that each element gives its own characteristic spectrum. No two elements can have identical line spectrum, as no two human beings have identical Finger-prints. Hence, line spectrum is also known as Finger-Print of atoms.

(b). ABSORPTION SPECTRUM
When the light from a source emitting a continuous spectrum is first passed through the substance taken in liquid form or gaseous form, and then passed through the prism the spectrum so obtained is known as Absorption Spectrum. In Absorption Spectrum some of the colors are missing which leave dark lines or bands at their places.
The Absorption Spectrum is further classified into Continuous Absorption Spectrum and Line Absorption Spectrum.
i) Continuous Absorption Spectrum
This type of spectrum arises when the absorbing material absorbs a continuous range of wavelengths. In this type of spectrum the dark lines overlap each other to form a continuous band.
ii) Line Absorption Spectrum
In this spectrum, sharp dark lines are obtained. This type of spectrum is obtained when the absorbing substance is in vapor state.

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