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

motion-and-stability-forces-and-interactions

Motion and Stability- Forces and Interactions

PS.PSc.6.2

Drift Velocity

Os elétrons livres em um condutor viajam em caminhos aleatórios e colidem com outros elétrons e partículas.
Em um campo elétrico, os elétrons que se movem aleatoriamente gradualmente se movem na direção oposta ao campo elétrico aplicado.
Assim, a velocidade média de partículas carregadas livremente em um material devido a um campo elétrico é conhecida como velocidade de deriva. É a razão entre a corrente em um condutor e o produto da concentração de partículas carregadas, a magnitude da carga de cada partícula e a área da seção transversal do condutor. A unidade SI de velocidade de deriva é metros por segundo.
Considere um fio de cobre com um diâmetro de 1 mm. Qual seria a velocidade média de deriva dos elétrons no fio quando uma corrente de 10 A passa por ele?
Para começar, calcule a densidade de elétrons livres no fio de cobre. O número de elétrons livres no cobre é igual ao número de átomos de cobre por metro cúbico. Em segundo lugar, calcule a área da seção transversal do fio.
Reorganizando e substituindo os termos, a velocidade de deriva pode ser determinada. O sinal negativo indica que as cargas se movem na direção oposta à corrente convencional.

<ol>
	<li>OpenStax. (2019). Física Universitária Vol. 2. [Versão da Web], pág. 95-96. Obtido 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>

velocidade de deriva

A alta velocidade dos sinais elétricos resulta do fato de que a força entre cargas age rapidamente a distância. Assim, quando uma carga livre é forçada para um fio, a carga que entra empurra outras cargas à frente, devido à força repulsiva entre cargas do mesmo tipo. Essas cargas em movimento movem as cargas mais adiante na linha. A densidade de carga em um sistema não pode ser facilmente aumentada, então o sinal é passado rapidamente. A onda de choque elétrico resultante se move pelo sistema quase à velocidade da luz. Para ser preciso, esse sinal rápido em movimento, ou onda de choque, é uma mudança propagando-se rapidamente no campo elétrico. Bons condutores possuem grandes números de cargas livres. Em metais, as cargas livres são elétrons livres. A distância que um elétron individual pode se mover entre colisões com átomos ou outros elétrons é bastante pequena. Os caminhos dos elétrons parecem, assim, quase aleatórios, como o movimento dos átomos em um gás. Mas existe um campo elétrico no condutor que faz com que os elétrons se desloquem na direção oposta (oposta ao campo, já que eles têm carga negativa). A velocidade média das cargas livres é conhecida como velocidade de deriva e é representada em metros por segundo. A velocidade de deriva é bastante pequena, da ordem de 10(-4) m/s, já que existem tantas cargas livres. As colisões de elétrons livres transferem energia para os átomos do condutor. O campo elétrico realiza trabalho ao mover os elétrons ao longo de uma distância, mas esse trabalho não aumenta a energia cinética dos elétrons.

As cargas das partículas em movimento podem ser positivas ou negativas, dependendo do tipo de material. Em metais, as cargas em movimento são negativas (elétrons), enquanto em um gás ionizado (plasma), as cargas em movimento podem incluir tanto elétrons quanto íons positivamente carregados. No caso de um material semicondutor, como o silício, a condução ocorre em parte por elétrons e em parte por buracos. Buracos são sítios de lacunas de elétrons perdidos, que agem como cargas positivas. A corrente convencional é tratada como um fluxo de cargas positivas, independentemente de as cargas livres no condutor serem positivas, negativas ou ambas; portanto, em um condutor metálico, as cargas em movimento são elétrons, mas a corrente ainda aponta na direção em que as cargas positivas fluiriam.

Velocidade de Deriva

A alta velocidade dos sinais elétricos resulta do fato de que a força entre as cargas atua rapidamente à distância. Assim, quando uma carga gratuita é forçada ...

Education

JoVE Core

Physics

Física

Unit 1

Unidade 1

Current and Resistance

Corrente e Resistência

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

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

Diode Current and Reverse Bias

A diode is a nonohmic circuit element that makes current and voltage behave differently from Ohm’s law. In most substances, current is proportional to the voltage applied, but a diode does not show a linear current-voltage relationship. A diode is a semiconducting device with two terminals: an anode, which is the positive terminal, and a cathode, which is the negative terminal. It allows current to flow in only one direction. In a simple circuit with a battery, a diode, and a resistor, the...

electrical power

Power Limits in Electrical Circuits

Electrical power in a circuit depends on current and voltage. It is the product of these two values and is measured in watts, or joules per second. That relationship helps explain how much energy a circuit can deliver. A car’s auxiliary power outlet is one real-world example. Some outlets are rated at 20 amps and 12 volts, so they can deliver a maximum of 240 watts. That rating shows the upper limit of power the circuit can provide to devices such as a cell phone charger. Bulb wattage also...

electrical energy

Cutting Electric Bills with Efficient Lighting

Electrical energy is the energy transferred when electrons move from one point to another. The longer an appliance is used, the more electrical energy it consumes. If power stays constant, electrical energy equals the power used by the device times the time it runs. That is why longer use leads to a higher electric bill. Electric bills measure this energy in kilowatt-hours. One kilowatt-hour is equal to 3.6 × 10^6 joules. You can lower electrical energy use by cutting the time an appliance...

continuity equation

Charge Conservation and Current Flow

Charge conservation and current flow are linked through the continuity equation. The current density is the amount of current flowing per unit cross-sectional area. The current through a surface can be written as a surface integral of the current density. The conservation of charge says that the total current leaving a volume equals the rate at which charge inside that volume decreases. The total charge can be written using volume charge density, which is a space function. Because of this, the...

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 - 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.PSc.6.3

PS.Phy.4.3

Tennessee Academic Standards

High School

Energy

PHYS.PS3.11

Virginia  Standards of Learning

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PS.9

PS.9.b

PS.9.c

PH.8

PH.8.b

Alabama Course of Study Science

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Waves and Their Applications in Technologies for Information Transfer

9-12.PS.2.3.c

9-12.PS.2.3.d

9-12.P.2.6.b

9-12.P.2.6.d

Florida Department of Education

SC.912.P.10

SC.912.P.10.15

Texas Essential Knowledge and Skills

PHYS.6

PHYS.6.D

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Energy

HS-PS3-6.

Position and Displacement

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Average Velocity

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Instantaneous Velocity - I

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Instantaneous Velocity - II

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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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Ohm's Law

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Construct an explanation to compare simple series and parallel circuits in terms of Ohm's Law.

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Torque On A Current Loop In A Magnetic Field

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Use models to explain magnetism in terms of domains, interactions of poles, and magnetic fields.

PS.PSc.6.4

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

Electrical Current and Electron Drift

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