Srit unit iii free electron theory engineering physics. Atomic selectrons are delocalised due to overlap of outer orbits. The development of the quantummechanical electron theory of metals. Amazingly, the conductivity predicted turns out to be the same as in the drude model, as it does not depend on the form of the electronic speed distribution. Mar 29, 2015 drude model of electrical conduction march 29, 2015 december 29, 2010 by mini physics drude model is a model in which the free electrons in a metal are treated like a classical ideal gas with a maxwellboltzmann distribution of kinetic energies, with an average thermal energy 32kt. Freeelectron theory of metals article about freeelectron. Below is a schematic diagram of drudes model of metals.
The drude theory of metals and the hall e ect by michele laino july 12, 2015 abstract in this brief tutorial i show the basic assumption of the drude model of conduction in metals, actually this tutorial represents a simpli ed version of the real drude model, since some properties, and. Mar 29, 2018 drude theory of conduction basics of free electron theory and electrical conductivity part 1. Metals drudes classical theory theory by paul drude in 1900, only three years after the electron was discovered. Classical free electron theory of metals engineering. In its more modern context, the drudelorentz model views a material as consisting of an array of the following. Drude formulated a theory for conduction in metals using the electron concept. The development of the quantummechanical electron theory of. The drude model of electrical conduction was proposed in 1900 by paul drude to explain the transport properties of electrons in materials especially metals. In drudes model, electrons transport heat because the electrons thermalized at the. The treatment of a metal as containing a gas of electrons completely free to move within it. According to this theory the free electrons obey quantum laws. The drude model can be visualised using the following simulation. Pdf drudelorentz model of semiconductor optical plasmons. Orlando february 9, 2004 the source of the binding energy is primarily the electrostatic potential between the nuclei and the electrons.
In the macroscopic maxwells equations, the total electric charge density r is factorized into a bound component rb and a free counterpart rf, just as the total current density j is separated into a free component jf and a bound component jb. Classical derivation of ohms law and drude conductivity. The free electrons are, therefore, also referred to as free electron gas and the theory is accordingly known as drude and lorentz s classical free electron theory. This variation of the optical parameters is attributed to the presence of free carriers. According to this theory, a metal consists of electrons which are free to move about in the crystal like molecules of a gas in a container. Arnold sommerfeld considered quantum theory and extended the theory to the free electron model, where the carriers follow fermidirac distribution. Metals drude s classical theory books metals drude s classical theory if you ally need such a referred metals drude s classical theory books that will give you worth, acquire the unquestionably best seller from us currently from several preferred authors. Drude model of electrical conduction march 29, 2015 december 29, 2010 by mini physics drude model is a model in which the free electrons in a metal are treated like a classical ideal gas with a maxwellboltzmann distribution of kinetic energies, with an average thermal energy 32kt. Below is a schematic diagram of drude s model of metals. The average distance of an electrons free movement between collisions is called the mean free path for metals, the mean free path is typically estimated as 1 nm based on known ionic packing parameters. To visualize a plasma oscillation, imagine a cube of metal placed in an external electric field pointing to the right. In the following we intend to show very accurately, both analytically and numerically, how the drude relation with.
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. Metalsdrudesclassicaltheory 11 pdf drive search and download pdf files for free. 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. Although the free electron model is a great oversimplification of the reality, surprisingly in many cases it works pretty well, so that it is able to describe many important properties of metals. Paul drude constructed in 1900 a theory to explain the electrical and ther. Drudes model 1900 is based on the kinetic theory of electrons in a metal which assumes that the material has motionless positive ions and a noninteracting electron gas. Drudelorentz theory drudelorentz theory drude in 1900. The defects of drude theory becomes more critical when we include. Metals and the drudelorentz model oxford scholarship. Application of kinetic theory to classical electron gas. The drude theory of metals the model assumptions and approximations collisionsare istantaneous change abruptly the electrons velocity assumed due to collision with ion cores electronelectronscatteringis not important thedetailedscattering mechanism is actuallynotimportant electrons trajectory scattering o the ionic cores.
Conductivity of materials, drudes theory and its failures nptel. Advanced electronic properties of materials classical drude theory of conduction contents. I drude model derivation of freeelectron conductivity i scattering time estimates and matthiessens rule i mobility and hall coe cients i frequencydependent conductivity. Classical free electron theory of metals this theory was developed by drude and lorentz and hence is also known as drude lorentz theory. As a result, the electrons acquire a constant velocity known as drift velocity. Jun 02, 2015 the drude model of electrical conduction was proposed in 190012 bypaul drude the model was extended in 1905 by hendrik antoon lorentz and hence is also known as the drudelorentz model and is a classical model. Free electrons in a metal resemble molecules of a gas. Drude theory of conduction basics of free electron theory and electrical conductivity part 1. These assumptions should be contrasted with those of the kinetic theory of conventional gases. Sommerfeld theory replaces f bv of drude s theory with fv profound consequences on and c v daniele to oli january 11, 2017 5 48. Drude applied equations of simple mechanics on the electrons to derive several expressions and also arrive at the ohms law. Drude treated the free electrons as a classical ideal gas but the electrons should collide with the stationary ions, not with each other. Drudes theory was used in order to calculate the freecarrier concentration and the mobilities, and these. Based on the drude model we arrive at the equation of motion for electrons in an.
The drude theory of metals and the hall e ect by michele laino july 12, 2015 abstract in this brief tutorial i show the basic assumption of the drude model of conduction in metals, actually this tutorial represents a simpli ed version of the real drude model, since some properties, and consequences, have been omitted. The classical free electron theory drude and lorentz proposed this theory in 1900. Drude treated the free electrons as a classical ideal gas. Lecture 2 drude theory of thermal conductivity the thermal. Derivation of the drude conductivity from quantum kinetic. Analytical and numerical demonstration of how the drude. Drude model of electrical conduction mini physics learn. The drude model assumes that the metal consists of immobile, positively charged ions and conducting free electrons that are unattached to the ions or atoms.
According to this theory, the metals containing the free electrons obey the laws of classical mechanics. The theory was originally proposed in 1900 to describe and correlate the electrical and thermal properties of metals. Assumptions the drude model considers the metal to be formed of a mass of positivelycharged ions from which a number of free electrons were detached. The localization energy can also play a role metal. The drude model of electrical conduction was proposed in 190012 bypaul drude the model was extended in 1905 by hendrik antoon lorentz and hence is also known as the drudelorentz model and is a classical model. Handout 1 drude model for metals cornell university. Drude constructed his theory of electrical and thermal conduction in metals by 1 considering the electrons to be a gas of negatively charged particles traversing in a medium of uniformly distributed positive ions, and 2 applying the kinetic theory of gas to the electron sea. It was constructed in order to explain the transport properties of conduction electrons in metals. Jun 06, 2008 im having trouble understanding the derivation of ohm s law from the drude model. The quantum free electron theory somerfield developed this theory in 1928. Although the free electron model is a great oversimplification of the reality, surprisingly in many cases it works pretty well, so that it is able.
Chapter 1 optical properties of plasmonic materials. Im having trouble understanding the derivation of ohms law from the drude model. Following drudes theory in context of drudes theory, then i will talk about dc. At room temperature, by using the kinetic theory of gases to estimate the drift velocity, the drude model gives. Drude theory of conduction basics of free electron theory. In most textbooks of solidstate physics, the drude formula is derived from either a classical. The relaxation time approximation here we treat electrons as a free ideal gas classical 2. Paul drude the theory of optics dover publications inc. I drude model derivation of freeelectron conductivity i scattering time estimates and matthiessens rule i mobility and hall coe cients i frequencydependent conductivity of freeelectron metals reading. The drude theory of metals the model free electron densities densityof the electron gas. Classical free electron theory of metals this theory was developed by drude and lorentz and hence is also known as drudelorentz theory. The drude formula of ac frequencydependent electric conductivity has been established as a simple and practically useful model to understand the electromagnetic response of simple freeelectronlike metals. Doitpoms tlp library introduction to thermal and electrical.
Drude model conductivity frequency dependence plasma waves difficulties of classical free electron model. Solid state physics part ii optical properties of solids. Drudes theory of electron transport was published in the year 1900 1, and is obviously based on classical physics. Classical theories classical theories refers to theories that predate modern, more complete, or more widely applicable theories. Drudelorentz model and was supplemented with the results of quantum theory in 1933 by arnold sommerfeld and hans bethe. This simple model uses classical mechanical theory of free electron. Classical derivation of ohm s law and drude conductivity. Theory of the free electron gas bgu physics department. Free electron model a free electron model is the simplest way to represent the electronic structure of metals. The only possible interaction of a free electron with its environment is via instantaneous. This is about the right order of magnitude for many monovalent metals, such as sodium.
Ohms law derivation from drude model physics forums. 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. Its extraordinary longevity owes to the fact that i for free electrons i. In drude model, due to kinetic theory of collision, that abruptly alter the velocity of an. Thermal properties of the free electron gas 1 groundstate properties of the electron gas 2 the fermidirac distribution 3 thermal properties of the free electron gas 4 the sommerfeld theory of conduction in metals daniele to oli january 11, 2017 27 48. With no applied field, it can be seen that the electrons move around randomly. The development of the quantummechanical electron theory. The model, which is an application of kinetic theory, assumes that the. Free electron theory of metals request pdf researchgate. The behaviour of free electrons moving inside the metals is considered to be similar to that of atoms or molecules in a perfect gas. Drude model conductivity frequency dependence plasma. Jun 30, 2018 the average distance of an electrons free movement between collisions is called the mean free path for metals, the mean free path is typically estimated as 1 nm based on known ionic packing parameters. Drude theory of conductivity university of illinois. Free electron theory of conductor was proposed by p.
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