Srit unit iii free electron theory applied physics. Shortly after the discovery of the electron by thomson in 1897, drude proposed a model of electrical conduction in metals as a kinetic theory of classical electrons. Metals drudes classical theory theory by paul drude in 1900, only three years after the electron was discovered. According to this theory, the metals containing the free electrons obey the laws of classical mechanics. Basic assumptions of drude model a gas of conduction electrons of mass m, which move against a background of heavy immobile ions electron density a z n m 0. Atomic selectrons are delocalised due to overlap of outer orbits. Ron ballinger gives todays lecture, explaining how the behavior of electrons in aggregate solids determines their electrical and thermal conductivities, optical absorption, and other physical properties. Pdf understanding of physics on electrical resistivity in. The experimental study of the optical properties of metals and the relation of the results to the drude free electron theory. In other words, the drude model is right about thermal conductivity, but wrong about heat capacity.
The classical free electron theory of metals drude lorentz theory of metals drude and lorentz proposed this theory in 1900. Apr 10, 20 the classical free electron theory ofmetals drude lorentz theory of metals lecture2postulates. The experimental study of the optical properties of metals. Hodgson 1 has found that the optical properties of mercury, unlike those of other liquid metals, cannot be explained in terms of the drude theory. Jun 15, 2018 this idea was given by drude and he utilized it to explain many properties of metals satisfactorily such as electrical conductivity, thermal conductivity etc. Apply to the dense electrons in metals by the free electron gas picture. The mechanical motion of electrons relative to atomic nuclei is modeled as a classical oscillator and used to predict properties such as the reflectance and dispersion of electromagnetic waves interacting with matter. Drude theory of metals university of california, irvine. Drude theory of metals problems in solid state physics. This is about the right order of magnitude for many monovalent metals, such as sodium.
In this letter we suggest that the backscattering of the electrons in mercury is so strong that, after a time of the order of the scattering time t, an electron tends to reverse its direction of. Theory by paul drude in 1900, only three years after the electron was discovered. The time between collisions with impurities is of order. Jun 02, 2015 timevarying analysis the dynamics may also be described by introducing an effective drag force accuracy of the model simple classical drude model provides a very good explanation of dc and ac conductivity in metal it greatly overestimates the electronic heat capacities of metals quantum theory quantum theory is a collection of results. Butler, electrical conduction in metals, physics today, 1978, 3112, 4449. Motivation metals are excellent conductors of heat and electricity, are ductile and malleable physicists have tried to construct simple models of the metallic state that account the characteristic metallic properties theory of paul drude in 1900 came only a few years after j. This gave the famous drude conductivity formula, 1. Drude lorentz theory drude, in 1900, postulated that the metals consist of positive ion cores with the valence electrons moving freely among these cores.
Binary systems with compounds ab melts incongruently at t 2 liquid composition is x, liquid fraction is zyzx x is a peritectic point 3 phases. Cu, be using lcaomo, and then extends this approach. The valence electrons of atoms are free to move about the whole volume of the metals like the molecules of a perfect gas in a container. Metals contain free electrons that move through a lattice of positive ions. Assumptions or salient features in classical free electron theory.
Plasma oscillations plasmons can be described in the classical picture as an oscillation of free electron density with respect to the fixed positive ions in a metal. The valence electrons of metallic atoms are free to move in the spaces between ions from one place to another place within the metallic specimen similar to. Drude model, 1900ad, after thompsons discovery of electrons in 1897. This textbook gives a complete account of electron theory in both periodic and nonperiodic metallic systems. System upgrade on feb 12th during this period, ecommerce and registration of new users may not be available for up to 12 hours. The model, which is an application of kinetic theory, assumes that the microscopic behaviour of electrons in a solid may be treated classically and looks much like a pinball machine, with a sea of constantly jittering electrons bouncing. Drude applied equations of simple mechanics on the electrons to derive several expressions and also arrive at the ohms law. Drudes model 1900 is based on the kinetic theory of electrons in a metal which. The simple approach is to regard the conduction band electrons as noninteracting electron gas and yields a fairly accurate description of metals like silver, gold or aluminium.
Chapter 5 the drude theory of metals basic assumption of drude model dc electrical conductivity of a metal hall effect thermal conductivity in a metal. The drude theory of metals the model kinetic theory of gases. For an historical survey of the contributions of physicist to the theory of metals, see p. The model, which is an application of kinetic theory, assumes that the microscopic behaviour of electrons in a solid may be treated classically and looks much like a pinball machine, with. Standard topics such as crystal structure, reciprocal space, free electrons, band theory, phonons, and magnetism are covered. The current theory explains this with ad hoc manipulations like screening and positive charge carriers, but the correct answer is much simpler. Handout 2 sommerfeld model for metals free fermion gas. Drude treated the free electrons as a classical ideal gas but the electrons should collide with the stationary ions, not with each other. One of the r easons is that the form of conductivity. Classical free electron theory of metals in order to explain electrical conductivity in metals, lorentz and drude put forward a theory called free electron theory of metals. In an atom electrons revolue around the nucleus and a metal is composed of such atoms.
Handout 1 drude model for metals cornell university. Deviations from the drude theory were observed, and the values of the optical mass and relaxation time of the conduction. The lorentz oscillator model shows that the response of a dielectric to an electric field may be described using the permittivity, and permeability, functions. Classical derivation of ohms law and drude conductivity. Electron conduction in a metal is an elementary subject treated in most textbooks of. This idea will have many applications, even beyond the drude model. Drude in 1900 and developed by lorentz in 1909 to explain electrical conduction in metals. Carrier dynamics of electrons and holes in moderately doped silicon pdf. Determination of plasma frequency, damping constant, and size. During last decades, the femtosecond laser ablation of noble metals was a subject of. This lecture series constitutes a first undergraduate course in solid state physics delivered in an engaging and entertaining manner by professor steven h. Pdf fractional drude model of electrons in a metal researchgate.
At room temperature, by using the kinetic theory of gases to estimate the. Ph208 drude model page 1 lecture1 drude model recap of kinetic theory of gases. Pdf understanding of physics on electrical resistivity in metals. The assumptions of the drudelorentz classical theory of freeelectrons are the following. Electrons in a metal behave much like particles in an ideal gas no coulombic interaction and no. Drudelorentz theory drudelorentz theory drude in 1900. The classical free electron theory was introduced by p. By paul drude, professor of physics at the university of giessen. The drude model peter hertel overview model dielectric medium permittivity of metals electrical conductors faraday e ect hall e ect paul drude, german physicist, 18631906. The drude and sommerfeld models of metals in other words, the collisions produce a frictional damping term. The drude model can be visualised using the following simulation. Introduction to the electron theory of metals the electron theory of metals describes how electrons are responsible for the bonding of metals and subsequent physical, chemical and transport properties. Elements can be more clearly classified as metals and non metals on the basis of their chemical properties. Lecture 1 drude model lecture1 drude model recap of kinetic.
The free electron model the quantum state of an electron is described by the timeindependent schrodinger equation. Drude theory and the optical properties of liquid mercury. Lorentz, the theory of electrons and its application to the phenomena of light and radiant heat, teubner. Pdf the essence of electrical resistivity in metal is discussed in detail mainly for physics. Millikan, assistant professors of physics at the university of chicago. Title derivation of the drude conductivity from quantum. We discuss these results with those obtained by tem microscopy. Chapter 5 the drude theory of metals delaware physics. Free electrons in a metal resemble molecules of a gas. The drude model of electrical conduction was proposed in 1900 by paul drude to explain the transport properties of electrons in materials especially metals. This model makes several key assumptions some of which are better approximations than others. Drude conductivity of a granular metal sciencedirect.
Normally the electrons are in a random motion throughout the. Generalized drude model and electromagnetic screening in. It features a 1hour lecture video, and also presents the prerequisites, learning objectives, reading assignment, lecture slides, homework with solutions, and resources for further study. Deriving the conductivity and permittivity of metals the drude model explains the electrodynamic properties of metals. In solidstate physics, the free electron model is a simple model for the behaviour of. Drude formulated a theory for conduction in metals using the electron concept. Then sommerfelds elementary quantum mechanical theory of metals is discussed. Generalized drude theory we start from the quasiclassical perspective of fluid mechanics, in which a fundamental equation is the euler equation where is the velocity field, p is the hydrodynamic pressure, n is the electron density, q and m represent electron charge and mass, and and are electric and magnetic fields respectively.
With no applied field, it can be seen that the electrons move around randomly. Veterans campground on big marine lake legislative position. Notes on the drude model assumptions of the drude model the drude model provides a classical mechanics approach to describing conductivity in metals. He derives the valence and conduction band structures for electrons in metals e. The freeelectron theory pioneered by drude and sommerfeld achieved a. Pdf free electron theory of metals aryan gurung academia. Free electron theory of metals rajendra adhikari december 9, 2015 1 drudes theory of metals in this model electrons are considered as solid spheres as gas.
Classical free electron theory of metals engineering. This page contains materials for the session on the band theory of solids. L z the electrons inside the box are confined in a threedimensional infinite. Drude theory of metals problems in solid state physics with. Veteranscampgroundonbigmarinelakereportlegacygrant170115. The electrons are, however, bound to move within the metal due to electrostatic attraction between the positive ion cores and the electrons. Jan 30, 2020 the drude theory a nd his formula o f the electrical c onductivity are still used in standard textbook of general physics and modern physics.
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