Name: magnetic flux and induced current
Uploaded: 2026-04-30T12:07:31.000Z
Duration: 1 min 16 s
Channel: JoVE

K12 Standards

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NC 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

Induction

Electromagnetic induction is produced when an electrically conducting material is exposed to a time-varying magnetic field.
For example, consider a bar magnet placed close to a coil. The galvanometer connected to this coil shows zero current passing through it.
If the bar magnet moves toward the coil, a current flows through the coil. Furthermore, if the bar magnet is moved away from the coil, current flows in the opposite direction.
Similarly, if the bar magnet is kept fixed and the coil is moved in either direction, then current flows through the coil.
Suppose a bar magnet is replaced with a second coil connected to a battery. If one of the coils is moved, a current flows through the other coil.&#xA0;
If a switch controls the current passing through the one coil, then an instantaneous current pulse is induced in the other coil while opening or closing the switch.
Here the current flowing through the other coil is called an induced current, and the corresponding emf is called an induced emf.

<ol>
	<li>Young, H.D e Freedman, R.A. (2012). Fisica universitaria con fisica moderna. San Francisco, CA: Pearson. Sezione 29.1, pagine 958-959.</li>
	<li>OpenStax. (2019). Fisica universitaria Vol. 2. [Versione web]. Sezione 13.1, pagine 582-585. Estratto da <a href="https://openstax.org/books/university-physics-volume-2/pages/13-1-faradays-law">https://openstax.org/books/university-physics-volume-2/pages/13-1-faradays-law</a></li>
</ol>

l'induzione

Un fem (forza elettromotrice) viene indotto quando il campo magnetico in una bobina viene modificato spingendo un magnete a barra dentro o fuori dalla bobina. Vengono prodotti fem di segno opposto dal moto in direzioni opposte, e le direzioni delle fem vengono invertite anche invertendo i poli. Gli stessi risultati si ottengono se la bobina viene mossa invece del magnete: &#xE8; il moto relativo che &#xE8; importante. Pi&#xF9; &#xE8; veloce il moto, maggiore &#xE8; la fem Inoltre, non c&#x27;&#xE8; fem quando il magnete &#xE8; fermo rispetto alla bobina.Un effetto simile pu&#xF2; essere prodotto utilizzando due circuiti, dove la corrente in un circuito induce una corrente in un secondo circuito vicino. Ad esempio, se un circuito portante corrente viene mosso verso o lontano dall&#x27;altro circuito stazionario, allora viene indotta una fem nell&#x27;altro circuito. Inoltre, se la corrente nel primo circuito &#xE8; controllata tramite un interruttore, allora l&#x27;apertura e la chiusura dell&#x27;interruttore inducono una fem nell&#x27;altro circuito.In tutti i casi sopra descritti, la fem indotta produce una corrente, chiamata corrente indotta. Il fattore comune in tutte queste osservazioni &#xE8; il cambiamento del flusso magnetico. Qui, il flusso magnetico sta cambiando, sia perch&#xE9; il campo magnetico dipende dal tempo o perch&#xE9; il moto del circuito cambia il flusso magnetico che lo attraversa. L&#x27;induzione avviene a causa della natura non statica delle forze coinvolte. Bisogna prestare attenzione durante l&#x27;analisi dei campi elettrici statici prodotti dalle distribuzioni di carica e dei campi elettrici non statici prodotti dai campi magnetici che variano nel tempo.

L'induzione

An emf is induced when the magnetic field in a coil is changed by pushing a bar magnet into or out of the coil. emfs of opposite signs are produced by ...

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Education

Didattica

JoVE Core

Physics

Fisica

Unit 1

Unità 1

Electromagnetic Induction

Induzione elettromagnetica

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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 still relative to each other, no emf is induced.

Induction can also happen between two nearby circuits. A current in one circuit can induce a current in the second circuit. If the current-carrying circuit moves closer to or farther from the other circuit, an emf is induced in the stationary circuit. Opening and closing a switch in the first circuit can also induce an emf in the second.

In each case, the key factor is changing magnetic flux. The flux changes because the magnetic field changes with time or because motion changes how much field passes through the circuit. The induced emf can then produce an induced current. Induction is tied to non-static forces, so static electric fields from charge distributions must be considered differently from electric fields caused by time-varying magnetic fields.

Magnetic Flux and Induced Current

induction

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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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...

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Eddy Currents and Magnetic Braking

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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...

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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...

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displacement current

Maxwell’s Fix for Changing Currents

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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...

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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

Explore how changing magnetic flux induces emf and current in coils and nearby circuits. Learn how motion, pole direction, and switches affect induction.

Magnetic Flux and Induced 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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PS.9

PS.9.a

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New York State Science Learning Standards

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Magnetic Flux and Induced Current

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