DIVERGENCE AND CURL OF POSITION VECTOR ' r '

MEISNER EFFECT ON SUPERCONDUCTORS

Meissner effect.

UNIT CELL AND LATTICE PARAMETERS

Unit cell In Crystals the arrangement of particles is described with three dimensional geometrical parallelepiped structure. The unit cell is defined as the smallest size of parallelepiped structure with minimum number of atoms. In a unit cell there are 6 faces and 8 corners. So 8 atoms are required to form a unit cell and all the 8 atoms are located at the 8 corners each. Lattice Lattice is defined as a three dimensional array of atoms. It describes the size and shape of the unit cell. Parameters of a unit cell A unit cell is described by six parameters. These parameters are three dimensions and the angles between them . The Dimensions of unit cell along three axes of a unit cell are represented by (a, b ,c) . The angle between b and c is represented by α, between a and c by β and between a and b by γ. we can identify the structure of crystal by knowing the parameters of unit cell. Properties of unit cell : 1. Unit cell is the minimum structure. 2. We can

BRAGG'S LAW - DIFFRACTION OF X-RAYS THOUGH CRYSTAL ALTTICE

Diffraction of X-rays through crystal lattice: (Bragg’s law) X-rays are used to identify the structure of a crystal. The property of diffraction of x-rays are used in this procedure. The wave length of ordinary light is very large comparing with the value of inter planar spacing. Hence ordinary light cannot penetrate trough the lattice planes. But X-rays penetrate through the lattice planes and they are scattered by the atoms of the crystal lattice. Each atom acts as an opaque and the distance between two atoms acts as narrow slit. Hence the crystal lattice is considered as diffraction grating. When x-rays are scattered by the successive parallel planes they diffract with each other and produce diffraction pattern.by studying the diffraction pattern we can find different sets of planes located in the lattice at different directions. Bragg used X-rays to study the structure of crystals. He derived the condition of maxima of diffraction pattern which is called

PHYSICS

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