Name: electrical current and electron drift
Uploaded: 2023-04-30T12:38:36.000Z
Duration: 1 min 19 s
Channel: JoVE

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Physical Science

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Motion and Stability- Forces and Interactions

PS.PSc.6.2

Drift Velocity

Les électrons libres d’un conducteur se déplacent sur des chemins aléatoires et entrent en collision avec d’autres électrons et particules.
Dans un champ électrique, les électrons se déplaçant de manière aléatoire dérivent progressivement dans la direction opposée au champ électrique appliqué.
Ainsi, la vitesse moyenne des particules chargées libres dans un matériau en raison d’un champ électrique est connue sous le nom de vitesse de dérive. Il s’agit du rapport entre le courant dans un conducteur et le produit de la concentration de particules chargées, de l’intensité de la charge de chaque particule et de la section transversale du conducteur. L’unité SI de la vitesse de dérive est le mètre par seconde.
Considérons un fil de cuivre d’un diamètre de 1 mm. Quelle serait la vitesse de dérive moyenne des électrons dans le fil lorsqu’un courant de 10 A le traverse ?
Pour commencer, calculez la densité d’électrons libres dans le fil de cuivre. Le nombre d’électrons libres dans le cuivre est égal au nombre d’atomes de cuivre par mètre cube. Deuxièmement, calculez la section transversale du fil.
En réarrangeant et en substituant les termes, la vitesse de dérive peut être déterminée. Le signe négatif indique que les charges se déplacent dans la direction opposée au courant conventionnel.

<ol>
	<li>OpenStax. (2019). Physique universitaire Vol. 2. [Version Web], p. 95-96. Tiré de <a href="https://openstax.org/books/university-physics-volume-2/pages/9-1-electrical-current">https://openstax.org/books/university-physics-volume-2/pages/9-1-electrical-current</a></li>
</ol>

vitesse de dérive

La vitesse élevée des signaux électriques résulte du fait que la force entre les charges agit rapidement à distance. Ainsi, lorsqu'une charge libre est forcée dans un fil, la charge entrante pousse les autres charges en avant en raison de la force répulsive entre les charges similaires. Ces charges en mouvement déplacent les charges plus loin sur la ligne. La densité de charge dans un système ne peut pas être facilement augmentée, donc le signal est transmis rapidement. L'onde de choc électrique résultante se déplace à travers le système presque à la vitesse de la lumière. Pour être précis, ce signal rapide, ou onde de choc, est un changement rapidement propagé dans le champ électrique. Les bons conducteurs ont de nombreux charges libres. Dans les métaux, les charges libres sont des électrons libres. La distance qu'un électron individuel peut parcourir entre les collisions avec des atomes ou d'autres électrons est assez petite. Les trajectoires des électrons apparaissent donc presque aléatoires, comme le mouvement des atomes dans un gaz. Mais il y a un champ électrique dans le conducteur qui fait dériver les électrons dans la direction opposée (opposée au champ puisqu'ils sont chargés négativement). La vitesse moyenne des charges libres est appelée vitesse de dérive et est représentée en mètres par seconde. La vitesse de dérive est assez faible, de l'ordre de 10-4 m/s, puisqu'il y a autant de charges libres. Les collisions des électrons libres transfèrent de l'énergie aux atomes du conducteur. Le champ électrique fait du travail en déplaçant les électrons sur une certaine distance, mais ce travail n'augmente pas l'énergie cinétique des électrons.

Les charges des particules en mouvement peuvent être positives ou négatives selon le type de matériau. Dans les métaux, les charges en mouvement sont négatives (électrons), tandis que dans un gaz ionisé (plasma), les charges en mouvement peuvent inclure à la fois des électrons et des ions chargés positivement. Dans le cas d'un semi-conducteur comme le silicium, la conduction est partiellement assurée par les électrons et les trous. Les trous sont des sites vacants d'électrons manquants, qui agissent comme des charges positives. Le courant conventionnel est considéré comme un flux de charges positives, indépendamment de savoir si les charges libres dans le conducteur sont positives, négatives ou les deux ; tandis que dans un conducteur métallique, les charges en mouvement sont des électrons, mais le courant indique toujours la direction où les charges positives s'écoulent.

Vitesse de dérive

La vitesse élevée des signaux électriques résulte du fait que la force entre les charges agit rapidement à distance. Ainsi, lorsqu’une charge gratuite est imposée ...

Education

Enseignement

JoVE Core

Physics

Physique

Unit 1

Unité 1

Current and Resistance

Courant et résistance

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

electrical current and electron drift

Electrical current in a conductor depends on moving charges and the tiny drift speed of those charges. When a free charge enters a wire, it pushes nearby charges ahead because like charges repel each other. That push spreads through the material very quickly, so the electrical signal moves through the system at nearly the speed of light.

This fast signal is not the same as the slow motion of each charge. It is a rapidly spreading change in the electric field, often described as an electrical shock wave. In a good conductor, there are many free charges available to carry that change along.

In metals, the free charges are free electrons. Each electron moves only a short distance before colliding with atoms or other electrons, so its path looks almost random. An electric field in the conductor gives the electrons a net drift in the direction opposite the field, because electrons are negatively charged.

The average speed of these free charges is called drift velocity. It is measured in meters per second and is very small, often around 10^-4 m/s, because so many free charges are present. Collisions transfer energy to the atoms of the conductor. The electric field does work on the electrons, but that work does not increase their kinetic energy.

The moving charges can be different in different materials. In metals, the charges are electrons. In an ionized gas, or plasma, the moving charges can include both electrons and positively charged ions. In a semiconductor such as silicon, conduction happens partly through electrons and holes, which are empty sites where electrons are missing and that act like positive charges.

Conventional current is treated as the flow of positive charge. This rule is used even when the real moving charges are negative, positive, or both. So in a metallic conductor, electrons move one way, but the current is still drawn in the direction that positive charges would move.

Electrical Current and Electron Drift

electrical current

Current Flow in Simple Circuits

Electrical current is the flow of charge in a circuit. A large current means a large amount of charge moves through a wire in a short time. A small current means only a small amount of charge moves through the circuit over a longer time. Examples include the current needed to run a refrigerator and the smaller current used by a handheld calculator. The SI unit for current is the ampere, or amp. It is named for the French physicist André-Marie Ampère (1775–1836). One ampere means one coulomb of...

drift velocity

Electrical current in a conductor depends on moving charges and the tiny drift speed of those charges. When a free charge enters a wire, it pushes nearby charges ahead because like charges repel each other. That push spreads through the material very quickly, so the electrical signal moves through the system at nearly the speed of light. This fast signal is not the same as the slow motion of each charge. It is a rapidly spreading change in the electric field, often described as an electrical...

current density

Current Density in Wires and Solutions

Current density describes how much electric current passes through a given cross-sectional area. It helps show not just the size of the current, but also how it is distributed through a conductor. The current density can change from point to point because the local charge flow can vary. If the current flow is uniform, the amount of current is the same at every point along the conductor, even when the conductor’s area changes. Current density is measured in amperes per square meter. Its...

resistivity

Resistivity in Conductors and Insulators

Resistivity describes how much a material opposes electric current. When a voltage is applied to a conductor, an electric field forms. The charges in the conductor feel that force, and a current density develops. In some materials, including metals at a given temperature, the current density is approximately proportional to the electric field. In those cases, current density can be modeled with conductivity, written as sigma. Electrical conductivity is measured in (ohm·m)^−1. It tells how well...

resistance

Factors That Affect Electrical Resistance

Electrical resistance describes how much a conductor opposes the flow of current. It is represented by R. When current passes through a conductor, heat is also produced. Resistance is tied to the material’s resistivity, which is a property of the material used to make an electrical component. Resistance is different from resistivity. Resistivity belongs to the material itself, while resistance belongs to the finished component. To study this relationship, consider a wire with length L,...

ohm's law

Measuring Current, Voltage, and Resistance

Ohm's law describes the relationship between current, voltage, and resistance in many materials. In these cases, the current through a substance is directly proportional to the voltage applied to it. The idea was first shown experimentally by German physicist Georg Simon Ohm, who studied current in a metal wire. A material, component, or device that follows this pattern is called ohmic. An ohmic component has a current that increases in step with voltage. A material or component that does not...

non-ohmic devices

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electrical power

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electrical energy

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boundary conditions for current density

Current Density at Conductivity Boundaries

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

Resistance and Ohm's Law in Conductors

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

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

Learn how electrical current travels through conductors, why electron drift is slow, and how metals, plasma, and semiconductors carry charge.

Electrical Current and Electron Drift | JoVE K12

physics

JoVE Core Physique présente plusieurs branches de la physique fondamentale grâce à des vidéos animées concises et faciles à comprendre ; cela inclut: la cinématique, la dynamique, la mécanique des fluides, la mécanique statique, les ondes et l'acoustique. En parallèle, les vidéos de scientifiques à l'action démontrent l'application de concepts associés à ces domaines dans des expériences de recherche classiques et originales réalisées dans des laboratoires modernes du monde entier.

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Waves and Their Applications in Technologies for Information Transfer

9-12.PS.2.3.c

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9-12.P.2.6.d

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New York State Science Learning Standards

HS. Energy

HS-PS3-6.

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Average Velocity

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Instantaneous Velocity - I

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PS.PSc.4.1

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Current Density

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Resistivity

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Resistance

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PS.PSc.6.4

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

Electrical Current and Electron Drift

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