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11 Dec 2011


1.  1. Diffraction Pattern
The non-uniform distribution of light energy obtained on the screen due to bending of lights rays at the corners or edges of the slit is called diffraction pattern.
2. Diffraction
The bending of light rays around the edges and corners of the obstacles is called diffraction.
3. Width of central maximum:- The width of central maximum is the linear distance between the first minima on the either side of central maxima of the diffraction pattern.
4. Fresnel’s distance the distance of screen from the slit at which the spreading of light becomes just equal to the size of the slit is called Fresnel’s distance.
There are two classes of diffraction
1.  Fresnel diffraction
2.  Fraunhofer diffraction

the diffraction pattern is due to a single rectangular slit consists of broad and intense central maximum and a number of narrower and fainter maxi-ma called secondary maxi-ma on the sides of central maxi ma. The width of central maximum is twice the width of fainter side maxi-ma.
5. An arrangement consisting of a large no. of equidistant narrow parallel rectangular slits of equal width separated by equal opaque portions called a diffraction grating.
6. The ratio of the change in angle of diffraction of any two neighboring spectral lines to their change in wavelength is called dispersive power.
7. Prism diffraction is due to refraction. Grating spectra is due to diffraction. Prism spectra has only one order and hence brighter. Grating spectra has different orders and so light is distributed to different orders.
8. Polarization tells us about the transverse nature of light waves.
9. The phenomenon in which light vibrations are confined to a single plane is called polarization of light.
10. Plane polarized light can be produced by reflection, refraction, and scattering.
11. Brewster’s law: the tangent of the angle of polarization for a given medium is numerically equal to the refractive index of medium. The angle at which the refracted ray from a transparent medium is plane polarized is called polarizing medium.
12. Pile of plates is used to produce polarized light by refraction.
13. Malus law: Malus law stated that when a completely plane polarized light is incident on a polarizing sheet the intensity of light transmitted through the analyzer varies as the square of cosine of the angle between the plane of transmission of the analyzer and the plane of polarizer.
14. When a light rays is passed through calcite or quartz crystal we get two defracted rays .one refracted rays obeys the laws of reflection and is called the ordinary ray or O-ray. The other ray does not obey the laws of refraction and is called the extraordinary ray or E-ray.
15. When a beam of unpolarised light is passed through certain       crystal like tourmaline , the light splits up into two beams,  polarized at right angles to each other; the light with vibrations perpendicular to optic axis are absorbed and the other components with vibrations parallel to the optic axis is transmitted. The selective absorption is called dichroism and the crystal are said to be diachronic.
16. Polaroid work on the principal of dichroism.
17. Polaroid are made by embedding the tiny synthetic crystals of harapathitewith their optical axis parallel in the transparent film of cellulose acetate.
18. Polaroid are used, in motor car head lights , in sunglasses, to view 3d pictures, as filters in photographic camera.

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