Name: how a dc generator makes current
Uploaded: 2023-09-18T17:11:20.000Z
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

Physics

motion-and-stability-forces-and-interactions

Motion and Stability- Forces and Interactions

PS.Phy.5.2

DC Generator

DC発電機は、機械エネルギーをDC電気エネルギーに変換します。DC発電機の基本的な構造は、2つのスリップリングが1つのスプリットリングに置き換えられることを除いて、単純なオルタネーターの構造と似ています。
導電ループが均一な磁場で回転すると、ループを通る磁束が正弦波に変化し、誘導起電力が発生します。
ここでは、分割リングが整流子として機能します。整流子は、ループの半回転ごとに接点を切り替え、誘導起電力の極性を同じにします。
オルタネーターと同様に、磁束が最大または最小のとき、誘導起電力はゼロです。
しかし、整流子のため、誘導起電力は決して負ではなく、磁束がゼロのときに最大になります。
平均誘導起電力の大きさは、単純なオルタネーターの正弦波項をその平均値に置き換えることによって推定されます。
誘導起電力の大きさは、特定の磁場の角速度とループの面積に比例します。

<ol>
	<li>ヤング、HD、フリードマン、RA(2012)。現代物理学と大学物理学。カリフォルニア州サンフランシスコ:ピアソン。セクション29.4、964-965ページ。</li>
</ol>

直流発電機

オルタネーターは、機械エネルギーを正弦波状に変化する電気エネルギーに変換し、AC 電流を生成します。 一方、DC 発電機は機械エネルギーを同じ極性の DC パルスである電気エネルギーに変換します。 DC 発電機の構造はオルタネータの構造と似ていますが、一対のスリップ リングが整流子とも呼ばれる単一の分割リングに置き換えられている点が異なります。 整流子は周期的なロータリー スイッチのように機能します。 導電ループが半回転するごとにブラシとの接触が変化し、誘導起電力が常に同じ極性になるようにします。

DC 発電機の基本的な動作原理は、ファラデーの誘導の法則に基づいています。 導電ループは均一磁場の中で回転し、この回転によりループを通過する磁束が周期的に変化します。 導電ループが外部回路に接続されると、変化する磁束によって起電力が誘導され、その結果誘導電流が発生します。 外部回路への接続は、整流子と一対のブラシを使用することを想定しています。

誘導起電力の大きさは、導電ループを通る磁束がゼロのときに最大となり、導電ループを通る磁束が最大または最小のときに最小になります。 磁束には正と負の値がありますが、誘導起電力は同じ極性を持ち、ゼロと最大の間で変動します。 誘導起電力の平均は、正弦波状に変化する成分の平均値を取ることによって計算されます。 誘導起電力の大きさは、印加される均一磁場、伝導ループの面積、回転の角速度を増加させることによって増加できます。

オルタネーターは、機械エネルギーを正弦波に変化する電気エネルギーに変換し、AC電流を生成します。一方、DC発電機は...

Education

JoVE Core

物理学

Unit 1

ユニット1

Electromagnetic Induction

電磁誘導

KEY TERMS AND CONCEPTS

主要用語と概念

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...

differential form of maxwell's equations

Maxwell’s Equations at a Point

Maxwell’s equations at a point describe how electric and magnetic fields change in space and time. They connect field behavior to charge and current density at a single location. This point-by-point form is useful when studying electromagnetic fields in detail. James Clerk Maxwell was a major physicist of the nineteenth century. He combined earlier laws of electricity and magnetism into one electromagnetic theory. The basic experimental laws came from scientists such as Oersted, Coulomb,...

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

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

Superconductor Critical Temperature

Superconductivity is the state in which a material has no electrical resistance and magnetic fields cannot penetrate it. A material that reaches this state is called a superconductor. The key idea in the transcript is the critical temperature, which is the temperature at which the change happens. Heike Kamerlingh Onnes of Leiden University first observed this behavior in mercury in 1911. He cooled a mercury sample in liquid helium to study how resistance changed with temperature. As the...

types of superconductors

Superconductors and Magnetic Levitation

Superconductors are materials that can carry electric current with zero resistance when they are cooled below a critical temperature. At this point, they also show the Meissner effect, which means they push magnetic fields out of their interior. A light permanent magnet can then levitate in a stable position above the superconducting sample. This magnetic levitation has real uses. High-speed trains have been built with strong superconducting magnets so they can float above the track and avoid...

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

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

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

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

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

physics

JoVE Core 物理学は、運動学、力学、流体力学、静力学、波動、音響などの基礎的な物理学の理論と応用を、簡潔でわかりやすいアニメーション ビデオで紹介します。さらに、科学者の実際のビデオでは、世界中の今日の研究所で行われている古典的および独自の研究実験における関連概念の適用を示しています。

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Electricity And Magnetism

Electromagnetic interactions

Tennessee Academic Standards

High School

Energy

PHYS.PS3.9

Virginia  Standards of Learning

HIgh School

Physical Science

PS.9

PS.9.f

Arizona Science Standards

HS+Phy.P2

HS+Phy.P2U1.1

Alabama Course of Study Science

waves-and-their-applications-in-technologies-for-information-transfer

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.

Simple Generator

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Projectile Motion: Equations

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Relative Velocity in One Dimension

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Relative Velocity in Two Dimensions

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Use models (graphs, equations, diagrams) to infer motion in two dimensions.

PS.Phy.1.2

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The first step in describing and analyzing most phenomena in physics involves the careful drawing of a free-body diagram. Free-body diagrams are useful in ...

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Use free body models to qualitatively and quantitatively analyze systems of forces in one dimension and two dimensions.

PS.Phy.2.1

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Newton's First Law: Application

Experience suggests that an object at rest remains at rest if left alone, and that an object in motion tends to slow down and stop unless some effort is ...

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Newton's Second Law

Newton&#39;s second law is closely related to his first law of motion. It mathematically gives the cause-and-effect relationship between force and changes ...

Carry out investigations to explain the interactions of forces on an object according to Newton's Laws of Motion.

PS.Phy.2.2

Analyze the motion of objects using time, distance, displacement, speed, velocity, and acceleration.

How a DC Generator Makes Current

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