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

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North Carolina K-12 Science Standard Course of Study

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Physical Science

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Motion and Stability- Forces and Interactions

PS.PSc.6.3

Theory of Metallic Conduction

Lorsqu'un champ électrique est appliqué à travers un conducteur, les électrons libres dérivent dans la direction opposée à la direction du champ tout en entrant en collision avec les ions du cristal.
Si le champ appliqué était nul, le mouvement aléatoire entraînerait, en moyenne, une dérive nette nulle car les collisions changeraient de direction de manière aléatoire. Le temps moyen entre les collisions est appelé temps libre moyen.
L'accélération de l'électron est donnée par la force électrique sur la masse. Son vecteur vitesse à tout instant est exprimé par le vecteur vitesse initial, l’accélération et le temps.
En faisant la moyenne des deux côtés sur les collisions, on obtient la vitesse moyenne. Cependant, comme la dérive moyenne due aux collisions est nulle, la vitesse de dérive est donnée par le produit de l’accélération et du temps libre moyen.
En utilisant la relation entre la densité de courant et la vitesse de dérive, la densité de courant est liée au champ électrique, qui est la loi d'Ohm.
Ainsi, la conductivité électrique est exprimée par le nombre d'électrons libres par unité de volume, la charge et la masse de l'électron, et le temps libre moyen.

<ol>
	<li>Young, H.D. et Freedman, R.A. (2012). La physique universitaire avec la physique moderne. San Francisco, Californie : Pearson ; l’article 25.6 ; Pages 838 et 839.</li>
	<li>Griffiths, David J. (1999). Introduction à l’électrodynamique (3e éd.). Upper Saddle River, New Jersey 07458 ; section 7.1.1 ; Pages 289 et 290.</li>
</ol>

théorie de la conduction métallique

La conduction des électrons libres à l'intérieur d'un conducteur est mieux décrite par la mécanique quantique. Cependant, un modèle classique fait des prédictions proches des résultats de la mécanique quantique. Il est appelé la théorie de la conduction métallique.

Dans cette théorie, la deuxième loi de Newton est utilisée pour déterminer l'accélération d'un électron en présence d'un champ électrique appliqué. Ensuite, sa vitesse est exprimée via cette accélération.

Un électron se déplace à travers le cristal, contenant des ions positifs, en collisionnant avec les ions. Ces collisions le dévient dans différentes directions. S'il n'y avait pas de champ électrique appliqué, la vitesse moyenne de l'électron serait nulle au cours des collisions. Cependant, en présence du champ électrique, l'électron accélère dans la direction opposée au champ entre les collisions, et donc la vitesse moyenne, appelée vitesse de dérive, est dans la direction du champ.

La durée moyenne entre les collisions est définie comme le temps libre moyen.

La relation entre la densité de courant et la vitesse de dérive relie la densité de courant au champ électrique. Cette relation est sous la forme de la loi d'Ohm, à partir de laquelle la conductivité électrique du matériau peut être obtenue.

Cette théorie prédit la dépendance correcte de la conductivité en fonction de la température. A mesure que la température du matériau augmente, les vibrations des ions augmentent, tout comme les collisions des électrons avec ces ions. Par conséquent, le temps libre moyen diminue, ce qui implique que la conductivité diminue. La prédiction selon laquelle la conductivité électrique du matériau diminue avec l'augmentation de la température est observée lors d'expériences, même si la dépendance exacte ne peut être trouvée qu'en utilisant la mécanique quantique seulement.

Théorie de la conduction métallique

La conduction des électrons libres à l’intérieur d’un conducteur est mieux décrite par la mécanique quantique. Cependant, un modèle classique fait des prédictions proches du ...

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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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Electrical Current and Electron Drift

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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

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Position and Displacement

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Average and Instantaneous Velocity Vectors

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Resistivity

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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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Magnetism

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Magnetic Flux

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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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PS.PSc.6.4

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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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