PGTRB:LATEST STUDY MATERIAL: PHYSICS: SPECTRA AND OPTICAL INSTRUMENTS.

PGTRB:LATEST STUDY MATERIAL: PHYSICS: SPECTRA AND OPTICAL INSTRUMENTS:

** 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.

** 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.