≈ K Carbon arc lamp ≈ K Lamp filament ≈ K 12th - 12th - - - - - Unit Electromagnetic waves emission spectrum. The emission spectrum can be divided into three types: (i) Continuous emission spectrum (or continuous spectrum) If the light from incandescent lamp (filament bulb) is allowed to pass through prism (simplest spectroscope), it splits up into seven colours. Thus, it consists of wavelengths containing all the visible colours ranging from violet to red (Figure . ).
Examples: spectrum obtained from carbon arc and incandescent solids. (ii) Line emission spectrum (or line spectrum): Suppose light from hot gas is allowed to pass through prism, line spectrum is observed (Figure . ). Line spectra are also known as discontinuous spectra.
The line spectra consists of sharp lines of definite wavelengths or frequencies. Such spectra arise due to excited atoms of elements. These lines are the characteristics of the element and are different for different elements. Examples: spectra of atomic hydrogen, helium, etc.
(iii) Band emission spectrum (or band spectrum) Band spectrum consists of several number of very closely spaced spectral lines which overlap together forming specific is called black body spectrum (Refer XI Physics Unit ). It is a continuous frequency (or wavelength) curve depending on the body’s temperature. Suppose we allow a beam of white light to pass through the prism (as shown in Figure . ).
It is split into its seven constituent colours which can be viewed on the screen as continuous spectrum. This phenomenon is known as dispersion of light and the definite pattern of colours obtained on the screen after dispersion is called as spectrum. The spectra can be broadly classified into two catagories: Figure . White light passed through prism – dispersion (a)Emission spectra When the spectrum of self luminous source is taken, we get emission spectrum.
Each source has its own characteristic Continuous spectrum Figure . continuous emission spectra Figure . line emission spectra Line spectrum Hot gas 12th - 12th - - - - - Unit