A bar magnet with its north pole pointing downward is...

Name: Problem 26, Chapter 23: Physics
Uploaded: 2021-02-22T20:09:21-08:00
Duration: 3 min 33 s
Channel: Eric Mockensturm
Description: A bar magnet with its north pole pointing downward is falling toward the center of a horizontal conducting ring. As viewed from above, is the direction of the induced current in the ring clockwise or counterclockwise? Explain.

A bar magnet with its north pole pointing downward is falling toward the center of a horizontal conducting ring. As viewed from above, is the direction of the induced current in the ring clockwise or counterclockwise? Explain.

Key Concepts

Electromagnetic Induction

Electromagnetic induction is the process by which a changing magnetic field creates an electric current in a conductive material. This phenomenon explains how movement or change in a magnetic field, such as that produced by a moving magnet, leads to the generation of an induced current in nearby conductors.

Faraday's Law

Faraday's Law states that the magnitude of the induced electromotive force (EMF) in a closed circuit is proportional to the rate of change of the magnetic flux through the circuit. It provides a quantitative framework for understanding how variations in magnetic fields translate into electrical voltages in a conductor.

Lenz's Law

Lenz's Law complements Faraday's Law by specifying the direction of the induced current. It dictates that the induced current will flow in such a direction that its own magnetic field opposes the change in the original magnetic flux. This opposition is a fundamental principle that helps maintain energy conservation in electromagnetic systems.

Magnetic Flux

Magnetic flux refers to the total magnetic field passing through a given area. It is a measure of the amount of magnetic field lines penetrating a surface, and changes in this flux—due to movement of a magnet or alterations in the magnetic field—are what instigate the induction of an electromotive force in conductive loops.

Transcript

00:01 So in this problem, we have a magnet that has the north pole towards this coil of wire down here, or this loop of wire, and it's falling.

00:15 And we're asked about what direction the current, the induced current in the loop of wire is, what direction it's flowing.

00:25 So what we can think about is that, you know, the magnetic field, the magnetic flux lines, around this magnet are given like this.

00:37 And then as this magnet falls towards this loop, the intensity of the magnetic field is going to increase.

00:47 Again, the magnetic flux lines are closer together.

00:51 You can think of them as closer together here or more dense here than they are, you know, away from the magnet.

00:58 So the magnetic field obviously decays away.

01:01 From the magnet here.

01:03 And so as the magnet gets closer to this loop of wire, the magnetic field, the magnitude is going to increase.

01:12 And so the physics says that the induced current will oppose that increase.

01:20 And so to change, to oppose that increase, we need a magnetic field that would be in the upwards direction here.

01:28 And from the right -hand rule, if we look at this whole system from the the top, again, this would be the south pole, the top of the magnet, which is the south pole.

01:36 Here's a loop of wire.

01:39 To have a magnetic field from the current that would oppose the magnetic field that's pointing down or into the page here, we need a magnetic field that's coming out of the page...

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