Name: how a dc generator makes current
Uploaded: 2023-09-18T17:11:20.000Z
Duration: 1 min 19 s
Channel: JoVE

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Physics

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Motion and Stability- Forces and Interactions

PS.Phy.5.2

DC Generator

Un generatore CC converte l'energia meccanica in energia elettrica CC. La costruzione di base del generatore CC è simile a quella del semplice alternatore, tranne per il fatto che i due collettori rotanti sono sostituiti con un unico anello diviso.
Quando l'anello conduttore ruota in un campo magnetico uniforme, il flusso magnetico attraverso l'anello cambia sinusoidalmente, provocando una forza elettromagnetica indotta.
In questo caso, l'anello diviso funge da commutatore. Il commutatore commuta i contatti per ogni mezza rotazione dell'anello, garantendo la stessa polarità per la f.e.m. indotta.
Simile a un alternatore, la f.e.m. indotta è zero quando il flusso magnetico è massimo o minimo.
Ma a causa del commutatore, la f.e.m. indotta non è mai negativa e ha un massimo quando il flusso magnetico è zero.
L'entità della quantità media indotta di campi elettromagnetici è stimata sostituendo il termine sinusoidale del semplice alternatore con il suo valore medio.
L'entità della f.e.m. indotta è proporzionale alla velocità angolare per il campo magnetico dato e l'area del loop.

<ol>
	<li>Young, H.D e Freedman, R.A. (2012). Fisica universitaria con fisica moderna. San Francisco, CA: Pearson. Sezione 29.4, pagine 964-965.</li>
</ol>

generatore dc

Un alternatore converte l'energia meccanica in energia elettrica che varia sinusoidalmente, risultando in una corrente alternata. Nel frattempo, un generatore di corrente continua converte l'energia meccanica in energia elettrica, che sono impulsi di corrente continua con la stessa polarità. La costruzione di un generatore di corrente continua è simile a quella di un alternatore, eccetto che la coppia di anelli collettori è sostituita da un singolo anello spezzato, chiamato anche commutatore. Il commutatore funziona come un interruttore rotante periodico; cambia i contatti con le spazzole per ogni mezza rotazione del circuito conduttore, garantendo che la f.m.i. indotta abbia sempre la stessa polarità.

Il principio di funzionamento base dei generatori di corrente continua si basa sulla legge di induzione di Faraday. Il circuito conduttore viene ruotato all'interno di un campo magnetico uniforme e questa rotazione cambia periodicamente il flusso magnetico che attraversa il circuito. Quando il circuito conduttore è collegato al circuito esterno, il cambiamento di flusso magnetico induce una f.m.i., che si traduce in una corrente indotta. Il collegamento al circuito esterno è realizzato utilizzando un commutatore e una coppia di spazzole.

La magnitudine della f.m.i. indotta è massima quando il flusso magnetico attraverso il circuito conduttore è zero e minima quando il flusso magnetico attraverso il circuito conduttore è massimo o minimo. Il flusso magnetico ha valori positivi e negativi, ma la f.m.i. indotta ha sempre la stessa polarità e oscilla tra zero e il massimo. La media della f.m.i. indotta è calcolata prendendo il valore medio della componente variabile sinusoidalmente. La magnitudine della f.m.i. indotta può essere aumentata aumentando il campo magnetico uniforme applicato, l'area del circuito conduttore e la velocità angolare della rotazione.

Generatore DC

Un alternatore converte l'energia meccanica in energia elettrica che varia sinusoidalmente, generando corrente alternata. Nel frattempo, un generatore CC converte ...

Education

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Electromagnetic Induction

Induzione elettromagnetica

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

how a dc generator makes current

A DC generator makes electrical energy from mechanical motion. It produces DC pulses with the same polarity, unlike an alternator, which gives sinusoidal AC current. The two machines have similar construction, but a DC generator uses a single split ring instead of a pair of slip rings.

That split ring is called a commutator. It works like a rotary switch that changes the contact with the brushes after each half turn of the conducting loop. This action keeps the induced emf at the same polarity, even as the loop keeps rotating.

The generator works by Faraday’s law of induction. A conducting loop turns inside a uniform magnetic field, so the magnetic flux through the loop changes over time. When the loop is connected to an external circuit, that changing flux induces an emf and then an induced current.

The commutator and brushes provide the link to the external circuit. The induced emf is largest when the magnetic flux through the loop is zero. It is smallest when the magnetic flux is at its maximum or minimum. The magnetic flux can change between positive and negative values, but the induced emf stays positive and varies between zero and a maximum value.

The average induced emf is found by averaging the sinusoidal part of the signal. Its size can be increased by making the uniform magnetic field stronger, increasing the area of the conducting loop, or increasing the angular velocity of rotation.

How a DC Generator Makes Current

induction

Magnetic Flux and Induced Current

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...

ampere-maxwell's law: problem-solving

Displacement Current in an RC Circuit

Displacement current in an RC circuit can be found by tracking the charging capacitor. A parallel-plate capacitor with capacitance C, plate area A, and plate separation d is connected to a resistor R and a battery of voltage V. When the current starts to flow at t = 0, the charge and voltage on the capacitor change with time. The first step is to use the RC-circuit result for the capacitor voltage at time t. With the z-axis pointing from the positive plate to the negative plate, the electric...

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dc generator

A DC generator makes electrical energy from mechanical motion. It produces DC pulses with the same polarity, unlike an alternator, which gives sinusoidal AC current. The two machines have similar construction, but a DC generator uses a single split ring instead of a pair of slip rings. That split ring is called a commutator. It works like a rotary switch that changes the contact with the brushes after each half turn of the conducting loop. This action keeps the induced emf at the same...

magnetic damping

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superconductor

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faraday's law

Magnetic Flux and Induced Emf

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lenz's law

Magnet Motion and Induced Current

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motional emf

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

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...

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

Eddy currents affect how metals move, stop, and heat up. They form only in conductors, so they are useful for separating metals from nonmetals and for other practical devices. In recycling centers, trash can be sent down a ramp under a strong magnet. Metals in the trash slow down because eddy currents resist their motion. Nonmetals keep moving, so the materials separate. This method works for metals in general, not only ferromagnetic ones. Eddy currents also help in metal detectors. A...

displacement current

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

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symmetry in maxwell's equations

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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

Motor Current and Speed Changes

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 DC generator uses a commutator, brushes, and magnetic flux changes to produce DC pulses from rotating motion and Faraday’s law.

How a DC Generator Makes Current | JoVE K12

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How a DC Generator Makes Current

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