Name: electron drift in metallic conduction
Uploaded: 2023-09-18T17:11:19.000Z
Duration: 1 min 17 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Physical Science

motion-and-stability-forces-and-interactions

Motion and Stability- Forces and Interactions

PS.PSc.6.3

Theory of Metallic Conduction

Quando um campo elétrico é aplicado em um condutor, os elétrons livres se deslocam na direção oposta à direção do campo enquanto colidem com os íons do cristal.
Se o campo aplicado fosse zero, o movimento aleatório resultaria, em média, em desvio líquido zero, pois as colisões mudariam aleatoriamente de direção. O tempo médio entre colisões é chamado de tempo livre médio.
A aceleração do elétron é dada pela força elétrica sobre a massa. Sua velocidade a qualquer momento é expressa pela velocidade inicial, pela aceleração e pelo tempo.
A média de ambos os lados sobre as colisões fornece a velocidade média. No entanto, como a deriva média devido a colisões é zero, a velocidade de deriva é dada pelo produto da aceleração e do tempo livre médio.
Usando a relação entre a densidade de corrente e a velocidade de deriva, a densidade de corrente está relacionada ao campo elétrico, que é a lei de Ohm.
Assim, a condutividade elétrica é expressa pelo número de elétrons livres por unidade de volume, a carga e a massa do elétron e o tempo livre médio.

<ol>
	<li>Young, H.D. e Freedman, R.A. (2012). Física Universitária com Física Moderna. São Francisco, CA: Pearson; seção 25.6; páginas 838–839.</li>
	<li>Griffiths, David J. (1999). Introdução à Eletrodinâmica (3ª ed.). Rio Upper Saddle, Nova Jersey 07458; Seção 7.1.1; páginas 289–290.</li>
</ol>

teoria da condutividade metálica

A condução de elétrons livres dentro de um condutor é melhor descrita pela mecânica quântica. No entanto, um modelo clássico consegue fazer previsões que são próximas aos resultados da mecânica quântica. Este modelo é chamado de teoria da condutividade metálica.

Nesta teoria, a segunda lei do movimento de Newton é usada para determinar a aceleração de um elétron na presença de um campo elétrico aplicado. Em seguida, sua velocidade é expressa por meio dessa aceleração.

Um elétron se move através do cristal, que contém íons positivos, e colide com os íons. Essas colisões o desviam em várias direções. Se não houvesse campo elétrico aplicado, a velocidade média do elétron seria zero ao longo das colisões. No entanto, na presença do campo elétrico, o elétron acelera em direção oposta ao campo entre as colisões, e assim a velocidade média, chamada velocidade de deriva, está na direção do campo.

O tempo médio entre as colisões é definido como o tempo médio livre.

A relação entre a densidade de corrente e a velocidade de deriva relaciona a densidade de corrente com o campo elétrico. Essa relação existe na forma da lei de Ohm, da qual a condutividade elétrica do material pode ser obtida.

Essa teoria prevê corretamente a dependência da condutividade em relação à temperatura. À medida que a temperatura do material aumenta, as vibrações dos íons aumentam e as colisões dos elétrons com esses íons também aumentam. Portanto, o tempo médio livre diminui, o que implica em uma diminuição na condutividade. A previsão de que a condutividade elétrica do material diminui com o aumento da temperatura é observada em experimentos, embora a dependência exata só possa ser encontrada usando a mecânica quântica.

Teoria da Condutividade Metálica

A condução de elétrons livres dentro de um condutor é melhor descrita pela mecânica quântica. No entanto, um modelo clássico faz previsões próximas ao ...

Education

JoVE Core

Physics

Física

Unit 1

Unidade 1

Current and Resistance

Corrente e Resistência

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

electron drift in metallic conduction

Electron drift in metallic conduction explains how free electrons move through a conductor. A classical model can describe this motion closely, even though quantum mechanics gives the best overall picture. This model is called the theory of metallic conduction.

In this theory, Newton's second law is used to find the acceleration of an electron when an electric field is applied. The electron's velocity is then found from that acceleration. The electron travels through a crystal of positive ions and collides with them. These collisions send the electron in different directions.

If no electric field is present, the average velocity of the electron is zero over many collisions. When an electric field is applied, the electron accelerates opposite to the field between collisions. As a result, the average velocity, called the drift velocity, points in the direction of the field. The average time between collisions is called the mean free time.

The link between current density and drift velocity gives the relationship between current density and electric field. This relationship has the form of Ohm's law, and it can be used to find the electrical conductivity of the material. The theory also predicts the correct temperature trend for conductivity.

As temperature rises, ion vibrations increase. Electrons then collide more often with the ions. The mean free time decreases, so the conductivity decreases. Experiments show this drop in conductivity with increasing temperature. The exact temperature dependence, however, requires quantum mechanics.

Electron Drift in Metallic Conduction

electrical current

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resistivity

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resistance

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ohm's law

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electrical power

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boundary conditions for current density

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Current density at a boundary changes when two conducting materials have different electrical conductivities. The normal component of current density stays continuous across the interface. The tangential component, which runs along the surface, becomes discontinuous across the boundary. Consider two conducting media with conductivities σ1 and σ2 separated by an interface. At point P1 in medium 1, the steady current density makes an angle α1 with the normal. At point P2 in medium 2, the current...

electrical conductivity

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Resistance and Ohm's law help explain how electric current moves through a conductor. In a perfect conductor, the electric field inside is zero because free electrons move to cancel it. Any extra charge then stays on the surface. In a practical conductor, an applied electric field can remain in place. That field drives electrons through the material and creates a current. The current density, which is current per unit area, is related to the electric field. More generally, it is related to the...

theory of metallic conduction

Electron drift in metallic conduction explains how free electrons move through a conductor. A classical model can describe this motion closely, even though quantum mechanics gives the best overall picture. This model is called the theory of metallic conduction. In this theory, Newton's second law is used to find the acceleration of an electron when an electric field is applied. The electron's velocity is then found from that acceleration. The electron travels through a crystal of positive ions...

key terms and concepts

Explore electron drift, mean free time, and conductivity in metallic conduction. See how electric fields and temperature affect current in metals.

Electron Drift in Metallic Conduction | JoVE K12

physics

JoVE Core - Fisica apresenta a teoria e a aplicação de tópicos fundamentais da física, incluindo cinemática, dinâmica, mecânica dos fluidos, estática, ondas e acústica, com vídeos animados concisos e de fácil compreensão. Além disso, os vídeos de cientistas em ação demonstram a aplicação de conceitos relacionados em experimentos de pesquisa clássica e original realizados nos laboratórios de todo o mundo hoje em dia.

PS.Phy.4.3

Virginia  Standards of Learning

HIgh School

PS.9

PS.9.b

PH.9

PH.9.e

Florida Department of Education

High School

SC.912.P.10

SC.912.P.10.14

Position and Displacement

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Electrical Current

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Drift Velocity

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Resistivity

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Resistance

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Non-ohmic Devices

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PS.PSc.6.2

Continuity Equation

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Boundary Conditions for Current Density

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Magnetic Fields

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Magnetic Field Lines

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motion-of-a-charged-particle-in-a-magnetic-field

Motion Of A Charged Particle In A Magnetic Field

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Magnetic Force On A Current-Carrying Conductor

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Magnetic Force Between Two Parallel Currents

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Magnetic Field Of A Current Loop

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Ampere's Law

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Solenoids

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Magnetic Field of a Solenoid

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Toroids

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PS.PSc.6.4

Induction

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Faraday's Law

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Lenz's Law

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PS.PSc.6.5

Analyze motion in terms of speed, velocity, acceleration, and momentum.

Electron Drift in Metallic Conduction

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