TYPES OF SPECTRA
Spectrum: It is the pattern of lines produced on the photographic plate, by the dispersion of a beam
when it is passed through the prism.
Spectrometer: It is the device used to record the spectrum.
Spectrograph It consists of source of light, Prism and photographic plate.
Spectra are of 2 types: 1. Emission spectrum 2. Absorption spectrum
Emission Spectrum:
When the substances are in the excited state they emit light. Spectrum obtained with this emitted
light is called emission spectrum.
Emission spectrum is obtained by heating the substances on a flame or by passing electric
discharge through the gases.
Emission spectrum consists of bright lines on dark background.
Absorption spectrum:
It is due to absorption of light.
When the substances are in the ground state, they absorb radiation and go to excited state, the
spectrum so obtained is called absorption spectrum.
Absorption spectrum consists of dark lines on bright background.
In the absorption spectrum lines are formed at same wavelengths as those of emission spectrum.
Emission spectrum or absorption spectrum is of two types.
Continuous spectrum or band spectrum:
In this spectrum formation of lines is continuous.
Each color fades in to the next color as in rainbow.
A beam of white light when passed through a prism, it gives a continuous spectrum of seven colors
i.e. VIBGYOR.
Incandescent lamp or hot solids at high temperatures will give continuous spectrum.
Discontinuous spectrum or line spectrum:
Line spectrum consists of sharp, distinct and well defined lines.
Gases or vapours of elements when heated in a flame or by passing electric discharge through
them, line spectrum is obtained.
Line spectrum is given by atoms and so it is called atomic spectrum.
Each element has it's own characteristic line spectrum, by which the element can be identified.
Band spectrum:
It consists of series of bands where each band is a group of lines merged together.
Band spectrum is given by molecules and so it is called molecular spectrum.
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