Name: faraday disk dynamo and dc output
Uploaded: 2023-09-18T17:11:16.000Z
Duration: 1 min 23 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.6.5

Faraday Disk Dynamo

Дисковая динамо-машина Фарадея представляет собой генератор постоянного тока, работающий по принципу индукции.
Он состоит из проводящего диска, вращающегося с постоянной угловой скоростью через проводящий вал, который помещен в равномерное магнитное поле перпендикулярно плоскости диска. Вращение диска индуцирует в нем движущуюся ЭДС.
Рассмотрим небольшой отрезок диска с вектором скорости, касательным к нему. Магнитная сила на этом сегменте направлена радиально наружу. При этом накапливаются свободные положительные заряды по направлению к ободу и свободные отрицательные заряды к центру, что приводит к ЭДС.
Интегрирование уравнения ЭДС в пределах длины сегмента и подстановка величины вектора скорости дает величину движущейся ЭДС.
Этот диск может быть подключен к цепи с помощью двух стационарных щеток, которые проводят ток по замкнутому контуру.
Согласно закону Ленца, индуцированный ток противостоит постоянной угловой скорости диска. Таким образом, необходимо проделать работу, чтобы диск вращался с постоянной угловой скоростью.

<ol>
	<li>Янг, Х.Д. и Фридман, Р.А. (2012). Университетская физика с современной физикой. Сан-Франциско, Калифорния: Пирсон. Раздел 29.4, страницы 971.</li>
</ol>

Диск Фарадея

Диск Фарадея – это постоянный во времени источник постоянного тока. Он состоит из проводящего диска, вращающегося с постоянной угловой скоростью в магнитном поле, в перпендикулярном плоскости диска. Вращение диска вызывает изменение магнитного потока, что приводит к возникновению (ЭДС), вызывающей развитие противоположных зарядов на ободе и в центре диска. Полярность индуцированной ЭДС может быть определена направлением магнитного поля и направлением вращения диска. Если вращающийся диск подключен к внешней цепи с помощью щёток, то возникающий ток будет протекать.

Согласно закону Ленца, индуцированная (ЭДС) всегда противодействует причине, вызывающей её возникновение. В случае диска Фарадея, индуцированная (ЭДС) противодействует вращению диска. Поэтому для поддержания постоянной угловой скорости вращения диска требуется подводить внешнюю энергию.

Индуцированная (ЭДС) в таком динамо-генераторе индуцированная (ЭДС) может составлять от нескольких милливольт до нескольких вольт. Величина индуцированной (ЭДС) может быть дополнительно увеличена путём подключения нескольких генераторов последовательно или путём увеличения магнитного поля, радиуса диска и угловой скорости вращения диска.

Дисковая динамо-машина Фарадея — это генератор постоянного тока, производящий постоянную во времени ЭДС. Он состоит из проводящего диска, который вращается с постоянным угловым углом ...

Education

JoVE Core

Physics

Физика

Unit 1

Раздел 1

Electromagnetic Induction

Электромагнитная индукция

KEY TERMS AND CONCEPTS

ОСНОВНЫЕ ТЕРМИНЫ И ПОНЯТИЯ

faraday disk dynamo and dc output

A Faraday disk dynamo is a DC generator that produces an emf constant in time. It uses a conducting disk that spins at constant angular velocity in a magnetic field. The magnetic field is perpendicular to the plane of the disk.

As the disk rotates, the magnetic flux changes and an emf is induced. This causes opposite charges to build up at the rim and at the center of the disk. The direction of the induced emf depends on the direction of the magnetic field and the direction of rotation.

If brushes connect the rotating disk to an external circuit, an induced current flows. Lenz’s law explains that the induced emf opposes the cause that creates it. In this case, the emf opposes the rotation of the disk, so outside power is needed to keep the disk moving at a constant angular velocity.

The induced emf in a Faraday disk dynamo can range from a few millivolts to a few volts. Its size can be increased by connecting multiple generators in series. It can also be raised by using a stronger magnetic field, a larger disk radius, or a faster disk rotation.

Faraday Disk Dynamo and DC Output

induction

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Magnetic flux and induced current are linked when a magnetic field changes near a coil. Moving a bar magnet into or out of a coil induces an emf, which is an electromotive force. If the motion goes in the opposite direction, the emf has the opposite sign. Reversing the magnet poles also reverses the direction of the induced emf. The same effect appears when the coil moves instead of the magnet. Relative motion is what matters. A faster motion produces a larger emf. If the magnet and coil stay...

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Displacement Current in an RC Circuit

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Magnetic Flux and Induced Emf

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lenz's law

Magnet Motion and Induced Current

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Induced Current from Changing Magnetic Flux

Induced current from changing magnetic flux depends on how a magnetic field interacts with an area. Magnetic flux changes when the field strength changes, when the area it passes through changes, or when the field turns relative to the surface. When any of these factors vary, the magnetic flux also varies. A change in area can happen in two common ways. The flux through a rectangular loop increases as the loop moves into a magnetic field. The magnetic flux through a rotating coil also changes...

faraday disk dynamo

A Faraday disk dynamo is a DC generator that produces an emf constant in time. It uses a conducting disk that spins at constant angular velocity in a magnetic field. The magnetic field is perpendicular to the plane of the disk. As the disk rotates, the magnetic flux changes and an emf is induced. This causes opposite charges to build up at the rim and at the center of the disk. The direction of the induced emf depends on the direction of the magnetic field and the direction of rotation. If...

induced electric fields

Faraday’s Law and Induced EMF

Faraday’s law explains how a changing magnetic flux can create an induced emf in a circuit. When current is induced, work is being done on the conduction electrons in the wire. That work must come from a source, and the source is not a battery or a magnetic field. A battery does not have to be present in a circuit for current to be induced. Magnetic fields also do not do work on moving charges. Instead, the change in magnetic flux produces an electric field in the wire. This is called an...

induced electric fields: applications

Electric Fields from Changing Magnetism

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eddy currents

Eddy Currents in Recycling, Brakes, and Heat

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Maxwell’s Fix for Changing Currents

Maxwell’s correction to Ampère’s law explains how changing electric fields can create magnetic fields. The key idea is the displacement current, Id, which Maxwell added to the real conduction current, I. This extra term helps the law work when current is not steady. The displacement current is defined using the permittivity of free space, ε0, and the electric flux, ΦE. It is not a real flow of charge. Instead, it is an added term in Maxwell’s equations that acts like current in Ampère’s law. <br...

significance of displacement current

Maxwell’s Fix for Charging Capacitors

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electromagnetic fields

Electric and Magnetic Fields in Motion

Electric and magnetic fields can come from different sources, but they can act in surprisingly similar ways. Static charges create electrostatic fields. These fields are conservative, which means a test charge does no net work after moving around a complete loop. Fields made by changing magnetic fields behave differently. They are not conservative, and they do net work on a charge. That work is proportional to how fast the magnetic flux changes. These fields also do not follow Gauss’s law for...

maxwell's equation of electromagnetism

Maxwell's Equations and Light Waves

Maxwell's equations bring electricity, magnetism, and light together in one electromagnetic theory. James Clerk Maxwell was a major nineteenth-century physicist, and his work helped shape modern physics. He also made important contributions to the kinetic theory of gases, color vision, and the study of Saturn's rings. Maxwell built on earlier experiments in electricity and magnetism from Oersted, Coulomb, Gauss, and Faraday. These physicists had discovered the basic laws separately. Maxwell...

symmetry in maxwell's equations

Electric and Magnetic Field Symmetry

Electric and magnetic field symmetry is a key part of Maxwell's equations. After the fields are calculated with Maxwell's four equations, the Lorentz force equation gives the force those fields exert on a charged particle moving at a certain velocity. The Lorentz force law combines the effect of the electric field and the magnetic field on the moving charge. Maxwell's equations and the Lorentz force law together describe electricity and magnetism. The symmetry in Maxwell's framework is easier...

electric generator: alternator

How Alternators Produce AC Power

Alternators produce alternating current by rotating a conducting loop in a magnetic field. As the loop turns inside the field, the magnetic flux through the coil changes with time. That changing flux induces an emf, or electric voltage, in the circuit. A simple alternator uses a loop placed in a uniform magnetic field. The loop connects to split rings, and brushes carry the current to the external circuit. As the loop rotates, the magnetic flux changes sinusoidally, so the induced emf also...

back emf

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Motor current and speed changes are linked by back emf in an electric motor. A motor sends current through a wire loop in a magnetic field. The magnetic field pushes on the loop and creates torque, which turns a shaft and does mechanical work. As the coil turns, the magnetic flux through it changes. That changing flux induces an emf, or voltage, by Faraday’s law. The motor then acts like a generator whenever its coil rotates, whether the shaft is turned by an external drive or by the motor...

key terms and concepts

Learn how a Faraday disk dynamo makes steady DC output, builds charge on the disk, and uses Lenz’s law to resist rotation.

Faraday Disk Dynamo and DC Output | JoVE K12

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Faraday Disk Dynamo and DC Output

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