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Lattice vibration

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  LATTICE VIBRATION:-      E very atom has a tendency to vibrate about their mean position at temperature above zero Kelvin. The mean position is referred as the Bravais lattice site . These vibrations occur due to interatomic interactions. As the atoms in the solids are present at lattice sites , so these vibrations are called lattice vibrations. Fig.1            Lattice vibration are the results of absorption of heat energy. A lattice is an array of atoms connected with each other by elastic springs or strings .      Here all the atoms present at lattice sites are coupled and the motion of one single atom is shared by the neighbouring atoms. Thus the crystal vibrates on a whole . The dynamic external forces which are responsible for the vibrations obey Hooke's law. It is assumed that the amplitude of the vibrations are small as compared to the interatomic spacing. Harmonic approximation is valid for lattice vibrations. T...
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Photoelectric effect

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Photoelectric effect: when light is incident on a metal surface then electrons are emitted from it. This phenomena is called photoelectric effect.The emitted electrons are called photoelectrons. Laws of photoelectric emissions : 1. The emission of photo-electrons takes place only when the frequency of incident radiation is above certain critical value of that metal.This critical value is called threshold frequency . 2 . The emission of photo-electrons starts as soon as the light falls on metal surface i.e.the photoelectric emission is instantaneous. 3 . The maximum kinetic energy with which the photo-electrons are emitted from a metal surface is independent of the intensity of the light and only depends upon the frequency. 4 . For a given frequency, the number of photo-electrons emitted is directly proportional to the intensity of incident light . 5 .The energy distribution of the photo-electron is independent of the intensity of the incident ...
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ELECTRIC POTENTIAL

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  Electric potential :-         C url of electrical field is zero therefore, electric field is conservative field. Scalar potential is defined only for conservative field.        In the following we first show that curl of electric field is zero . We know field of a point charge at the origin.      If we take the integral along a closed path Then, . Apply Stoke theorm   Here,  This result can be generalised for any charge distribution using the principal of superposition. The general result is 
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