Name: electrical current and electron drift
Uploaded: 2023-04-30T12:38:36.000Z
Duration: 1 min 19 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.6.2

Drift Velocity

אלקטרונים חופשיים במוליך נעים בנתיבים אקראיים ומתנגשים עם אלקטרונים וחלקיקים אחרים.
בשדה חשמלי, האלקטרונים הנעים באופן אקראי נסחפים בהדרגה בכיוון ההפוך לשדה החשמלי המופעל.
לפיכך, המהירות הממוצעת של חלקיקים טעונים חופשיים בחומר עקב שדה חשמלי ידועה כמהירות הסחיפה. זהו היחס בין הזרם במוליך למכפלה של ריכוז החלקיקים הטעונים, גודל המטען של כל חלקיק ושטח החתך של המוליך. יחידת SI של מהירות הסחיפה היא מטרים לשנייה.
שקול חוט נחושת בקוטר של 1 מ"מ. מה תהיה מהירות הסחיפה הממוצעת של האלקטרונים בחוט כאשר זרם של 10 אמפר עובר דרכו?
כדי להתחיל, לחשב את צפיפות האלקטרונים החופשיים בחוט הנחושת. מספר האלקטרונים החופשיים בנחושת שווה למספר אטומי הנחושת למטר מעוקב. שנית, חשב את שטח החתך של החוט.
על ידי סידור מחדש, והחלפת התנאים, ניתן לקבוע את מהירות הסחיפה. הסימן השלילי מציין כי המטענים נעים בכיוון ההפוך לזרם הקונבנציונלי.

<ol>
	<li>OpenStax. (2019). פיזיקה אוניברסיטאית כרך 2. [גרסת אינטרנט], עמ' 95-96. מקור: <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>

מהירות סחיפה

<div style="direction:rtl">המהירות הגבוהה של אותות חשמליים נובעת מהעובדה שהכוח בין מטענים פועל במהירות במרחק. לפיכך, כאשר מטען חופשי נאלץ לתוך חוט, המטען הנכנס דוחף מטענים אחרים קדימה בגלל כוח הדחייה בין מטענים דומים. מטענים נעים אלה מרחיקים את המטענים לאורך הקו. לא ניתן להגדיל בקלות את צפיפות המטען במערכת, ולכן האות מועבר במהירות. גל ההלם החשמלי שנוצר עובר במערכת כמעט במהירות האור. ליתר דיוק, האות הנע הזה, או גל ההלם, הוא שינוי המתפשט במהירות בשדה החשמלי. למוליכים טובים יש מספר גדול של חיובים חופשיים. במתכות, המטענים החופשיים הם אלקטרונים חופשיים. המרחק שאלקטרון בודד יכול לנוע בין התנגשויות עם אטומים או אלקטרונים אחרים הוא קטן למדי. נתיבי האלקטרונים נראים אפוא כמעט אקראיים, כמו תנועת אטומים בגז. אבל יש שדה חשמלי במוליך שגורם לאלקטרונים להיסחף בכיוון ההפוך (מנוגד לשדה, שכן הם טעונים שלילי). המהירות הממוצעת של המטענים החופשיים ידועה כמהירות הסחף והיא מיוצגת במטרים לשנייה. מהירות הסחף היא די קטנה, בסדר גודל של 10−4 m/s, מכיוון שיש כל כך הרבה טעינות חופשיות. התנגשויות אלקטרונים חופשיות מעבירות אנרגיה לאטומים של המוליך. השדה החשמלי אכן פועל בהזזת האלקטרונים למרחק, אך עבודה זו אינה מגבירה את האנרגיה הקינטית של האלקטרונים. המטענים של החלקיקים הנעים עשויים להיות חיוביים או שליליים בהתאם לסוג החומר. במתכות, המטענים הנעים הם שליליים (אלקטרונים), בעוד שבגז מיונן (פלזמה), המטענים הנעים עשויים לכלול גם אלקטרונים וגם יונים בעלי מטען חיובי. במקרה של מוליך למחצה כמו סיליקון, ההולכה היא בחלקה על ידי אלקטרונים וחורים. חורים הם כמה אתרים פנויים של אלקטרונים חסרים, הפועלים כמו מטענים חיוביים. לזרם הקונבנציונלי מתייחסים כזרימה של מטענים חיוביים, ללא קשר אם המטענים החופשיים במוליך הם חיוביים, שליליים או שניהם; בעוד שבמוליך מתכתי, המטענים הנעים הם אלקטרונים, אך הזרם עדיין מצביע בכיוון של מטענים חיוביים שיזרמו.</div>

המהירות הגבוהה של אותות חשמליים נובעת מכך שהכוח בין מטענים פועל במהירות מרחוק. לכן, כאשר תשלום חינם מאולץ ...

Education

JoVE Core

Physics

פיזיקה

Unit 1

יחידה 1

Current and Resistance

זרם והתנגדות

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

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 Physics introduces the theory and application of fundamental physics topics, including kinematics, dynamics, fluid mechanics, statics, waves, and acoustics, with concise and easy-to-understand animated videos. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

PS.PSc.6.3

PS.Phy.4.3

Tennessee Academic Standards

High School

Energy

PHYS.PS3.11

Virginia  Standards of Learning

HIgh School

PS.9

PS.9.b

PS.9.c

PH.8

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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

The position of an object defines its location relative to a convenient frame of reference at any particular time. A frame of reference is an arbitrary ...

Average Velocity

To calculate the other physical quantities in kinematics, we must introduce the time variable. The time variable allows us not only to state the position ...

Instantaneous Velocity - I

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Instantaneous Velocity - II

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Average Acceleration

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Position and Displacement Vectors

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average-and-instantaneous-velocity-vectors

Average and Instantaneous Velocity Vectors

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Acceleration Vectors

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Linear Momentum

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Analyze and interpret data to explain the motion of an object moving with a constant velocity or that is accelerating.

PS.PSc.4.1

Electrical Current

Electrical current is defined as the rate at which charge flows. When there is a large current present, such as that used to run a refrigerator, a large ...

The high speed of electrical signals results from the fact that the force between charges acts rapidly at a distance. Thus, when a free charge is forced ...

Current Density

The total amount of current flowing through one unit value of a cross-sectional area is referred to as current density. If the current flow is uniform, ...

Resistivity

When a voltage is applied to a conductor, an electrical field is generated, and charges in the conductor feel the force due to the electrical field. The ...

Resistance

When a current moves through any conductor, the conductor causes some level of difficulty for the current to flow. The measure of that difficulty is known ...

Ohm's Law

Many materials exhibit a simple relationship between the values of current, voltage, and resistance, known as Ohm&#8217;s law. The current that flows ...

Non-ohmic Devices

In most substances, the current flow is proportional to the voltage applied to it. A simple relationship between the values of current, voltage, and ...

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

Continuity Equation

The total amount of current flowing per unit cross-sectional area is called the current density. Hence, the current passing through a cross-sectional area ...

Boundary Conditions for Current Density

Current density becomes discontinuous across an interface of materials with different electrical conductivities. The normal component of the current ...

Electrical Conductivity

In perfect conductors, the electric field inside is always zero due to the abundance of free electrons, which nullify any field by flowing. As a result, ...

Theory of Metallic Conduction

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Obtain, evaluate, and communicate information to explain how current is affected by changes in composition, length, temperature, and diameter of wire.

Magnetism

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Magnetic Fields

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Magnetic Field Lines

The representation of magnetic fields by magnetic field lines is very useful in visualizing the strength and direction of the magnetic field. Each of the ...

Magnetic Flux

The magnetic flux measures the number of magnetic field lines passing through a given surface area. The SI unit for magnetic flux is the weber (Wb). ...

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

Motion Of A Charged Particle In A Magnetic Field

A charged particle experiences a force when moving through a magnetic field. Consider the field to be uniform and the charged particle to move ...

Magnetic Force

In addition to the electric forces between electric charges, moving electric charges exert magnetic forces on each other. A magnetic field is created by a ...

magnetic-force-on-a-current-carrying-conductor

Magnetic Force On A Current-Carrying Conductor

Moving charges experience a force in a magnetic field. Since the magnetic fields produced by moving charges are proportional to the current, a conductor ...

magnetic-force-on-current-carrying-wires-example

Magnetic Force On Current-Carrying Wires: Example

In a magnetic field, moving charges encounter a force. If a wire contains these moving charges, i.e., if the wire is carrying a current, then a force acts ...

force-on-a-current-loop-in-a-magnetic-field

Force On A Current Loop In A Magnetic Field

Magnetic forces on wires carrying current are most frequently applied in motors. A DC motor is a device that converts electrical energy into mechanical ...

torque-on-a-current-loop-in-a-magnetic-field

Torque On A Current Loop In A Magnetic Field

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The Hall Effect

Edwin H. Hall, in the year 1879, devised an experiment that could be used to identify the polarity of the predominant charge carriers in a conducting ...

Magnetic Field due to Moving Charges

A stationary charge creates and interacts with the electric field, while a moving charge creates a magnetic field.
Consider a point charge moving with a ...

Biot-Savart Law

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Biot-Savart Law: Problem-Solving

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Consider a mobile phone battery ...

Magnetic Field Due to Two Straight Wires

Consider two parallel straight wires carrying a current of 10 A and 20 A in the same direction and separated by a distance of 20 cm. Calculate the ...

magnetic-force-between-two-parallel-currents

Magnetic Force Between Two Parallel Currents

Two long, straight, and parallel current-carrying conductors exert a force of equal magnitude on one another. The direction of the force depends on the ...

Magnetic Field Of A Current Loop

Consider a circular loop with a radius a, that carries a current I. The magnetic field due to the current at an arbitrary point P along the axis of the ...

Divergence and Curl of Magnetic Field

The magnetic field due to a volume current distribution given by the Biot&#8211;Savart Law can be expressed as follows:

To evaluate the divergence of the ...

Ampere's Law

A fundamental property of a static magnetic field is that it is not conservative, unlike an electrostatic field. Instead, there is a relationship between ...

Ampere's Law: Problem-Solving

Ampere&#x27;s law states that for any closed looped path, the line integral of the magnetic field along the path equals the vacuum permeability times the ...

Solenoids

A solenoid is a conducting wire coated with an insulating material, wound tightly in the form of a helical coil. The magnetic field for a solenoid is the ...

Magnetic Field of a Solenoid

A solenoid is a conducting wire coated with an insulating material, wound tightly in the form of a helical coil. The magnetic field due to a solenoid is ...

Toroids

A toroid is a closely wound donut-shaped coil constructed using a single&#xA0; conducting wire. In general, it is assumed that a toriod consists of ...

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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