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  • Spectra can  be classified into two principal classes known as emission spectra and absorption spectra.
  • An emission spectrum is obtained, when light emitted by a source is examined with a spectrometer.
  • Absorption spectrum is obtained when the light emitted from a source is made to pass through an absorbing material and then examined with a spectrometer.
  • There are three types of emission spectra (i) Continuous emission spectra (ii) Line spectra (iii) band spectra.
  • Every source has its emission spectrum.
  • Continuous emission spectra are not characteristic of the emitting substance, but depends only on the temperature.
  • The line emission spectra are emitted by atoms in the gaseous state.
  • The line emission spectra of a gas can be used to identify the gas.
  • Band emission spectra are obtained from molecules.
  • Each molecule has its own characteristics band emission spectrum.
  • As in the case of emission spectra, we may classify absorption spectra as (i) continuous (ii) line and (iii) band absorption spectra.
  • Fraunhofer dark lines are founds in solar spectrum.
  • The heating effect of the infrared radiations is used in measuring the wavelength of the radiation.
  • The colour of the sky is due to the scatting of sunlight.
  • The shorter wavelengths are scattered much more than the longer wavelengths.
  • The sun looks reddish at sunset and sunrise.
  • Raman effect can be explained using the quantum theory of radiation.
  • The laser light is coherent, monochromatic, and extremely intense.
  • The stimulated emission is very important in LASER.
  • Spectrometer is an instrument to study the spectra of different sources of light and the refractive indices of materials.
  • The name of the spectrum which is produced by an incandescent sources at high temperature is a continuous spectrum.
  • A line spectrum identified a gas.
  • The spectrum produced by a substance in molecular state is known as band spectrum.
  • The dark lines in the solar spectrum are called Fraunhofer lines.
  • The heating effect of these radiations is used in measuring the wavelength of the infrared radiations 
  • The blue colour of the sky is due to the scattering of shorter wavelength of the solar spectrum.
  • Raman effect supports Quantum theory.
  • The very important phenomenon in LASER is stimulated emission.
  • In normal population the number of atoms in the ground state is more.
  •  The process of population inversion is to increase the number of atoms in the excited state.
  • The significance of i-d curve as a prism is to find out angle of incidence.
  • The unit of refractive index of a medium is no unit.
  • The refractive index of the prism is calculated using the formula Mu=sin(A+D)/2/Sin(A/2).
  • There is an apparent change in the frequency of light radiation when the source or the observer moves with respect to one another. This phenomenon is known as Doppler effect.
  • It consists pf unbroken luminous bands all wavelengths containing all the colours from red to violet. The colours present depend upon the temperature of the source is continuous spectra.
  • The line spectra are emitted by atoms in the gaseous state. These are sharp lines of define wavelength.
  • Band spectra are obtained from molecules and it consists of a series of bands with a sharp edge at one end but fading out at the other end.
  • The wavelengths of the IR are measured in microns, represented by Mu. 1Mu =10^-6metre.
  • The heating effect of the infra-red radiations is used in measuring the wavelength of the radiation.
  • The spectrum consists of lines of greater wavelength called Stoke's lines and lines of shorter wavelength called Antistoke's lines.
  • Laser is used in eye surgery because it seals small blood vessels they cut through.
  • Laser beams are used to generate three dimensional images of objects in a process called holography.

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