Question

Explain the types of emission spectrum.

Answer 1

When the spectrum of self-luminous sources is taken, we get the emission spectrum. Each source has its own characteristic emission spectrum. The emission spectrum can be divided into three types:

1. Continuous emission spectra (or continuous spectra):
   If the light from the incandescent lamp (filament bulb) is allowed to pass through a prism (simplest spectroscope), it splits into seven colours. Thus, it consists of wavelengths containing all the visible colours ranging from violet to red.
   Examples: spectrum obtained from carbon arc, incandescent solids, liquids gives continuous spectra.
   
   Continuous emission spectra

2. Line emission spectrum (or line spectrum):
   Suppose light from hot gas is allowed to pass through prism, line spectrum is observed. Line spectra are also known as discontinuous spectra. The line spectra are sharp lines of definite wavelengths or frequencies.

   Such spectra arise due to excited atoms of elements. These lines are the characteristics of the element which means it is different for different elements.
   Examples: spectra of atomic hydrogen, helium, etc.
   
   line emission spectra

3. Band emission spectrum (or band spectrum):
   Band spectrum consists of several very closely spaced spectral lines which overlapped together forming specific bands which are separated by dark spaces, known as band spectra. This spectrum has a sharp edge at one end and fades out at the other end.

   Such spectra arise when the molecules are excited. Band spectrum is the characteristic of the molecule hence, the structure of the molecules can be studied using their band spectra. Examples, spectra of hydrogen gas, ammonia gas in the discharge tube etc.