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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North Carolina K-12 Science Standard Course of Study

9-12

Physical Science

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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.

induction

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 motion in opposite directions, and the directions of emfs are also reversed by reversing poles. The same results are produced if the coil is moved rather than the magnet&#x2014;it is the relative motion that is important. The faster the motion, the greater the emf. Additionally, there is no emf when the magnet is stationary relative to the coil.
A similar effect can be produced using two circuits, where the current in one circuit induces a current in a second, nearby circuit. For example, if a current-carrying circuit is moved toward or away from the other stationary circuit, then emf is induced in the other circuit. Additionally, if the current in the first circuit is controlled via a switch, then opening and closing of the switch induces an emf in the other circuit.
In all the above scenarios, the induced emf induces a current, called an induced current. The common factor in all these observations is changing magnetic flux. Here, the magnetic flux is changing, either because the magnetic field is time-dependent or because the motion of the circuit changes the magnetic flux passing through it. Induction occurs because of the non-static nature of the forces involved. Careful consideration must be given while analyzing static electric fields produced with charge distributions and non-static electric fields produced due to time-varying magnetic fields.

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

JoVE Core

Physics

Unit 1

Electromagnetic Induction

KEY TERMS AND CONCEPTS

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

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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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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Maxwell’s Fix for Changing Currents

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electromagnetic fields

Electric and Magnetic Fields in Motion

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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...

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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

physics

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

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Virginia  Standards of Learning

HIgh School

PS.9

PS.9.a

PS.9.e

Minnesota Academic Standards in Science

1.2.1 9C.4.2.1.1

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New Jersey Student Learning Standards for Science

Motion and Stability: Forces and Interactions

HS-PS2-5

Arizona Science Standards

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HS+Phy.P2U1.1

Alabama Course of Study Science

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9-12.PS.2.3.e

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PHYS.6.C

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New York State Science Learning Standards

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Magnetic Flux and Induced Current

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