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

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Physics

motion-and-stability-forces-and-interactions

Motion and Stability- Forces and Interactions

PS.Phy.5.2

DC Generator

A DC generator converts mechanical energy into DC electrical energy. The basic construction of the DC generator is similar to that of the simple alternator, except that the two slip rings are replaced with a single split ring.
As the conducting loop rotates in a uniform magnetic field, the magnetic flux through the loop changes sinusoidally, resulting in induced emf.
Here the split ring acts as a commutator. The commutator switches the contacts for each half rotation of the loop, ensuring the same polarity for the induced emf.
Similar to an alternator, the induced emf is zero when the magnetic flux is either maximum or minimum.
But because of the commutator, the induced emf is never negative and has a maximum when the magnetic flux is zero.
The magnitude of the average induced emf is estimated by replacing the sinusoidal term from the simple alternator with its average value.
The magnitude of the induced emf is proportional to the angular velocity for the given magnetic field and the area of the loop.

dc-generator

Een dynamo zet mechanische energie om in elektrische energie die sinusoïdaal varieert, wat resulteert in wisselstroom. Ondertussen zet een DC-generator mechanische energie om in elektrische energie, dit zijn DC-pulsen met dezelfde polariteit. De constructie van een DC-generator is vergelijkbaar met die van een dynamo, behalve dat het paar sleepringen is vervangen door een enkele splitring, ook wel commutator genoemd. De commutator functioneert als een periodieke draaischakelaar; het verandert de contacten met de borstels voor elke halve rotatie van de geleidende lus, waardoor de geïnduceerde emf altijd dezelfde polariteit heeft. Het fundamentele werkingsprincipe van DC-generatoren is gebaseerd op de inductiewet van Faraday. De geleidende lus wordt binnen het uniforme magnetische veld geroteerd, en deze rotatie verandert de magnetische flux die periodiek door de lus gaat. Wanneer de geleidende lus is aangesloten op het externe circuit, induceert de veranderende magnetische flux een emf, wat resulteert in een geïnduceerde stroom. De verbinding met het externe circuit wordt gerealiseerd met behulp van een commutator en een paar borstels. De grootte van de geïnduceerde emf is maximaal wanneer de magnetische flux door de geleidende lus nul is en minimaal wanneer de magnetische flux door de geleidende lus maximaal of minimaal is. De magnetische flux heeft positieve en negatieve waarden, maar de geïnduceerde emf heeft dezelfde polariteit en schommelt tussen nul en maximum. Het gemiddelde van de geïnduceerde emf wordt berekend door de gemiddelde waarde van de sinusoïdaal variërende component te nemen. De omvang van de geïnduceerde emf kan worden vergroot door het aangelegde uniforme magnetische veld, het gebied van de geleidende lus en de hoeksnelheid van de rotatie te vergroten.

DC-generator

An alternator converts mechanical energy into electrical energy that varies sinusoidally, resulting in AC current. Meanwhile, a DC generator converts ...

Education

JoVE Core

Natuurkunde

Unit 1

Onderdeel 1

Electromagnetic Induction

Elektromagnetische inductie

KEY TERMS AND CONCEPTS

BELANGRIJKE TERMEN EN CONCEPTEN

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

Eddy Currents and Magnetic Braking

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Superconductor Critical Temperature

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faraday's law

Magnetic Flux and Induced Emf

Faraday’s law connects magnetic flux changes to induced emf, or voltage. A change in the magnetic field or in the coil’s orientation with respect to the field can produce this voltage. Magnetic flux describes how many magnetic field lines pass through a given surface area.

lenz's law

Magnet Motion and Induced Current

Magnet motion and induced current are linked by Lenz’s law. The law says that the induced emf, or electromotive force, drives current around a wire loop in a direction that opposes the change in magnetic flux that caused it. A moving bar magnet can create this effect in a coil. If the magnet moves toward the coil, the magnetic flux increases and an induced current appears. That current produces a magnetic field that pushes against the stronger field from the magnet. The same idea works in...

motional emf

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faraday disk dynamo

Faraday Disk Dynamo and DC Output

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induced electric fields

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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

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displacement current

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significance of displacement current

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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

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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 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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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.

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Ohio’s Learning Standards and Model Curriculum

Electricity And Magnetism

Electromagnetic interactions

Tennessee Academic Standards

High School

Energy

PHYS.PS3.9

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Physical Science

PS.9

PS.9.f

Arizona Science Standards

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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.e

Florida Department of Education

SC.912.P.10

SC.912.P.10.16

Texas Essential Knowledge and Skills

PHYS.6

PHYS.6.B

Chemistry and Physics

IPC.6

IPC.6.B

Georgia Standards of Excellence

SPS10.

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How a DC Generator Makes Current

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