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

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Motion and Stability- Forces and Interactions

PS.Phy.5.2

DC Generator

DC 발전기는 기계적 에너지를 DC 전기 에너지로 변환합니다. DC 발전기의 기본 구조는 두 개의 슬립 링이 단일 분할 링으로 대체된다는 점을 제외하고는 간단한 교류 발전기의 기본 구조와 유사합니다.
전도 루프가 균일한 자기장에서 회전할 때 루프를 통한 자속이 정현파로 변경되어 유도 emf가 발생합니다.
여기서 분할 링은 정류자 역할을 합니다. 정류자는 루프의 각 절반 회전에 대한 접점을 전환하여 유도 된 emf에 대해 동일한 극성을 보장합니다.
교류 발전기와 유사하게, 유도 emf는 자속이 최대 또는 최소일 때 0입니다.
그러나 정류자 때문에 유도 된 emf는 결코 음수가 아니며 자속이 0 일 때 최대치를 갖습니다.
평균 유도 emf의 크기는 단순 교류 발전기의 정현파 항을 평균 값으로 대체하여 추정됩니다.
유도 된 emf의 크기는 주어진 자기장과 루프의 면적에 대한 각속도에 비례합니다.

<ol>
	<li>Young, H.D 및 Freedman, RA (2012). 현대 물리학을 가진 대학 물리학. 샌프란시스코, 캘리포니아 : 피어슨. 섹션 29.4, 964-965페이지.</li>
</ol>

dc 발전기

교류발전기는 기계적 에너지를 정현파로 변화하는 전기 에너지로 변환하여 AC 전류를 생성합니다. 한편, DC 발전기는 기계적 에너지를 동일한 극성의 DC 펄스인 전기 에너지로 변환합니다. DC 발전기의 구성은 한 쌍의 슬립 링이 정류자라고도 불리는 단일 분할 링으로 대체된다는 점을 제외하면 교류 발전기의 구성과 유사합니다. 정류자는 주기적인 회전 스위치처럼 기능합니다. 이는 전도 루프의 각 반 회전마다 브러시와의 접촉을 변경하여 유도된 EMF가 항상 동일한 극성을 갖도록 보장합니다.

DC 발전기의 기본 작동 원리는 패러데이의 유도 법칙을 기반으로 합니다. 전도성 루프는 균일한 자기장 내에서 회전하며, 이 회전으로 인해 루프를 통과하는 자속이 주기적으로 변경됩니다. 전도 루프가 외부 회로에 연결되면 변화하는 자속이 EMF를 유도하여 유도 전류가 발생합니다. 외부 회로에 대한 연결은 정류자와 한 쌍의 브러시를 사용하여 구상됩니다.

유도 EMF의 크기는 전도 루프를 통과하는 자속이 0일 때 최대이고 전도 루프를 통과하는 자속이 최대 또는 최소일 때 최소입니다. 자속은 양의 값과 음의 값을 가지지만 유도된 EMF는 동일한 극성을 가지며 0과 최대 사이에서 변동합니다. 유도된 EMF의 평균은 정현파로 변하는 성분의 평균값을 취하여 계산됩니다. 유도된 EMF의 크기는 적용된 균일한 자기장, 전도 루프의 면적 및 회전의 각속도를 증가시킴으로써 증가될 수 있습니다.

DC 발전기

교류 발전기는 기계적 에너지를 정현파로 변하는 전기 에너지로 변환하여 AC 전류를 생성합니다. 한편, DC 발전기는 ...

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Unit 1

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Electromagnetic Induction

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KEY TERMS AND CONCEPTS

주요 용어 및 개념

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...

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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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Eddy currents can create strong drag on moving objects. This drag is called magnetic damping. A metallic pendulum bob swinging between the poles of a strong magnet feels this force as it enters and leaves the field, so its motion dies out quickly. The effect is much smaller for a slotted metal plate. As the plate enters the magnetic field, a changing flux induces an emf, or electromotive force. The slots limit the size of the current loops, and nearby loops can carry currents in opposite...

superconductor

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faraday's law

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lenz's law

Magnet Motion and Induced Current

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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

An electric field can be induced by a changing magnetic field. This induced electric field is nonconservative, which means it does not do net work when a charge moves around a closed path. That behavior is different from an electrostatic field, which comes from a fixed charge distribution. An electrostatic field is conservative, so it does no net work over a closed path. Because of this difference, electric potential can be linked to the electrostatic field, but not to the induced field. When...

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

Maxwell’s fix for a charging capacitor is the displacement current in Ampère’s law. A displacement current is not a flow of charge like conduction current. It comes from a changing electric field. That is why it is defined using a time-varying electric field and has its own displacement current density. Maxwell added this term to the original Ampère’s law. The result is called generalized Ampère’s law. The added displacement current term lets the law work in regions where no charges are moving.

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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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

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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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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Waves and Their Applications in Technologies for Information Transfer

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How a DC Generator Makes Current

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