Name: magnetic poles and everyday uses
Uploaded: 2023-04-30T12:40:25.000Z
Duration: 1 min 30 s
Channel: JoVE

K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Physical Science

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Motion and Stability- Forces and Interactions

PS.PSc.6.4

Magnetism

O magnetismo foi observado pela primeira vez há mais de 2500 anos, perto da antiga cidade de Magnésia.
Os ímãs podem ser encontrados em objetos do dia a dia, como alto-falantes, cartões de crédito, bússolas e dispositivos de memória.
Uma barra magnética tem um pólo norte e um pólo sul. Quando um prego de ferro não magnetizado é colocado em contato com ele, ele se torna magnetizado.
Como pólos de um ímã se repelem, enquanto pólos diferentes se atraem.
Os pólos de um ímã não podem ser separados quebrando-os em dois pedaços. Em vez disso, ímãs menores, cada um com uma extremidade norte e sul, são obtidos. Portanto, monopolos magnéticos nunca são observados.
Em uma bússola de navegação, a agulha é uma barra magnética fina suspensa em seu centro.
O pólo norte de uma bússola é atraído para perto do pólo norte geográfico da Terra.
A Terra também age como uma enorme barra magnética, com seu pólo sul magnético perto do pólo norte geográfico e seu pólo norte magnético perto do pólo sul geográfico.
O eixo do ímã da Terra e o eixo geográfico não coincidem. Esse desvio é chamado de declinação magnética.

<ol>
	<li>OpenStax. (2019). Física Universitária Vol. 2. [Versão da Web], seção 11.1, páginas 494–496. Obtido de <a href="https://openstax.org/books/university-physics-volume-2/pages/11-1-magnetism-and-its-historical-discoveries">https://openstax.org/books/university-physics-volume-2/pages/11-1-magnetism-and-its-historical-discoveries</a></li>
</ol>

magnetismo

Imãs são comumente encontrados em objetos do dia a dia, como brinquedos, cabides, elevadores, campainhas e dispositivos de computador. Experimentos com esses ímãs demonstram que todos eles têm dois polos: um é chamado de norte (N) e o outro sul (S). Os polos magnéticos se repelem se forem iguais e se atraem se forem diferentes. Além disso, ambos os polos de um ímã atraem pedaços de ferro não magnetizados.

Um polo magnético individual não pode ser isolado. Independentemente de quão pequeno seja, cada peça de um ímã contém um polo norte e um polo sul. Essa propriedade dos ímãs difere da propriedade das cargas elétricas, em que tanto as cargas positivas quanto as negativas podem existir isoladamente.

Um exemplo de ímã é uma agulha de uma bússola. Este é um ímã em forma de barra fina suspenso em seu centro, para que possa girar livremente em um plano horizontal. A Terra também age como um ímã gigante, com seu polo atraído pelo sul localizado próximo ao seu Polo Norte geográfico. O polo norte de uma bússola é atraído para o Polo Norte geográfico da Terra porque o Polo Norte geográfico da Terra está próximo de seu polo sul magnético.

Em 1819, o físico dinamarquês Hans Oersted estava realizando uma demonstração durante uma palestra para alguns estudantes e percebeu que uma agulha de bússola se movia sempre que a corrente fluía em um fio próximo. Investigações adicionais desse fenômeno convenceram Oersted de que uma corrente elétrica poderia, de alguma forma, causar uma força magnética.

Atualmente, o magnetismo desempenha muitos papéis importantes em nossas vidas. O entendimento dos físicos sobre o magnetismo possibilitou o desenvolvimento de tecnologias que afetam tanto indivíduos quanto a sociedade. Por exemplo, o tablet eletrônico que cabe na bolsa ou mochila não seria possível sem as aplicações do magnetismo e da eletricidade em pequena escala.

Todos os motores elétricos contêm ímãs. Geradores, seja produzindo energia hidrelétrica ou acendendo luzes de bicicleta, usam campos magnéticos. Instalações de reciclagem usam ímãs para separar o ferro de outros resíduos. A pesquisa sobre o uso da contenção magnética da fusão como uma futura fonte de energia tem continuado por vários anos. A ressonância magnética nuclear (MRI) se tornou uma ferramenta diagnóstica importante no campo da medicina, e o uso do magnetismo para explorar a atividade cerebral é um tema de pesquisa e desenvolvimento contemporâneo. A lista de aplicações também inclui discos rígidos de computador, gravação em fita, detecção de amianto inalado e levitação de trens de alta velocidade.

Magnetismo

Os ímãs são comumente encontrados em objetos do cotidiano, como brinquedos, cabides, elevadores, campainhas e dispositivos de computador. A experimentação com esses ímãs mostra ...

Education

JoVE Core

Physics

Física

Unit 1

Unidade 1

Magnetic Forces and Fields

Forças e Campos Magnéticos

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

magnetic poles and everyday uses

Magnetism appears in many everyday objects, from toys and hangers to elevators, doorbells, and computer devices. Magnets have two poles, called north and south. Like poles repel each other, while unlike poles attract. Both poles can also attract unmagnetized iron. A single magnetic pole cannot be isolated, because every part of a magnet contains both a north pole and a south pole.

A compass needle is a simple example of a magnet. It is a thin bar magnet suspended at its center, so it can turn freely in a horizontal plane. Earth also behaves like a giant magnet. Its south-seeking pole is near the geographic North Pole. That is why the north end of a compass points toward Earth’s geographic North Pole, which is close to Earth’s magnetic south pole.

The link between electricity and magnetism became clear in 1819. During a lecture demonstration, Danish physicist Hans Oersted noticed that a compass needle moved when current flowed in a nearby wire. Further study showed that an electric current can create a magnetic force. This discovery helped scientists connect electric currents with magnetic effects.

Magnetism is important in many modern technologies. Electric motors contain magnets, and generators use magnetic fields to produce power, including hydroelectric power and bicycle lights. Recycling facilities use magnets to separate iron from other waste. Magnetism also supports MRI, computer hard drives, tape recording, detection of inhaled asbestos, research on brain activity, and the levitation of high-speed trains. Work on magnetic containment for fusion energy is also ongoing.

Magnetic Poles and Everyday Uses

magnetism

Magnetism appears in many everyday objects, from toys and hangers to elevators, doorbells, and computer devices. Magnets have two poles, called north and south. Like poles repel each other, while unlike poles attract. Both poles can also attract unmagnetized iron. A single magnetic pole cannot be isolated, because every part of a magnet contains both a north pole and a south pole. A compass needle is a simple example of a magnet. It is a thin bar magnet suspended at its center, so it can turn...

magnetic fields

Magnetic Force on Moving Charges

Magnetic force on moving charges depends on motion, charge, and field direction. A moving charge or a current creates a magnetic field in the space around it, along with its electric field. That magnetic field can then push on other moving charges or currents in the field. A magnetic field is a vector field, so it has direction as well as strength. At any point, the field direction is the direction a compass needle’s north pole points. The field strength is defined from the force a charged...

magnetic field lines

Reading Magnetic Field Lines

Magnetic field lines show the direction and strength of a magnetic field. They make it easier to picture how a magnet acts in space. Each line forms a closed loop around the magnet. For a bar magnet, the field lines leave the north pole and curve around to the south pole. They then continue through the magnet back to the north pole. This loop has no beginning or end. Magnetic field lines follow clear rules. The magnetic field points tangent to a field line at any point. A small compass points...

magnetic flux

Magnetic Flux Through Surfaces

Magnetic flux through a surface describes how much magnetic field passes across that surface. It is measured in weber (Wb), the SI unit for magnetic flux. Magnetic flux is a scalar quantity, not a vector. Three factors shape magnetic flux. They are the magnetic field strength B, the area the field crosses, and the orientation of the field relative to the surface. For a small area element dA, the flux depends on the part of the magnetic field that is normal, or perpendicular, to that element at...

motion of a charged particle in a magnetic field

motion-of-a-charged-particle-in-a-magnetic-field

Charged Particle Paths in Magnetic Fields

A charged particle in a magnetic field follows a path that depends on the direction of its velocity. When the field is uniform and the particle moves perpendicular to it, the magnetic field is the main factor that controls the motion, especially in a vacuum. The magnetic force is always perpendicular to the direction of motion, so the particle curves into a circle. Because the force stays perpendicular to velocity, it does no work on the particle. The kinetic energy and speed stay constant...

magnetic force

Magnetic Fields and Moving Charges

Magnetic fields and moving charges create magnetic force. A moving electric charge, or a current made of many moving charges, produces a magnetic field. When another current or moving charge enters that field, it feels a magnetic force in response. At the atomic level, magnetic forces come from interactions between moving electrons in the atoms of two bodies. The strength of magnetic force depends on several factors. It increases with the size of the charge and with the strength of the...

magnetic force on a current-carrying conductor

magnetic-force-on-a-current-carrying-conductor

Current and Magnetic Field Around a Wire

A current-carrying wire creates a magnetic field around it, and moving charges feel a force in that field. Because the magnetic field produced by moving charges is proportional to current, the wire itself acts as a source of magnetic field. A compass placed near the wire shows this effect by lining up tangentially around the wire. The magnetic field around a straight wire forms concentric circular loops. The right-hand rule helps determine the direction of those loops. If the thumb points in...

magnetic force on current-carrying wires: example

magnetic-force-on-current-carrying-wires-example

Balancing Weight with Magnetic Force

Magnetic force can balance the weight of a current-carrying wire when the wire sits in a magnetic field. Moving charges in the wire feel a force, so the wire itself can be pushed upward or downward. This example uses a flexible wire that is 40 cm long and has a mass of 10 g. It is held in a horizontal position inside a constant 0.40 T magnetic field. The goal is to find the current needed to remove the tension in the supporting leads. To do that, a free-body diagram is drawn first. The diagram...

force on a current loop in a magnetic field

force-on-a-current-loop-in-a-magnetic-field

Current Loops and Torque in Motors

Current loops in a magnetic field create the torque that drives a DC motor. A DC motor converts electrical energy into mechanical work. In a motor, wire loops sit inside a magnetic field. When current flows through the loops, the magnetic field pushes on them and makes the shaft rotate. The current is reversed when the loop lines up with the magnetic field. This keeps the torque on the loop going in the same direction. A commutator and brushes handle this reversal. The commutator switches the...

torque on a current loop in a magnetic field

torque-on-a-current-loop-in-a-magnetic-field

Current Loop Torque in Electric Motors

Current loop torque in electric motors shows how magnetic force can make a wire loop rotate. In an electric motor, loops of wire sit between magnets in a magnetic field. When current flows through the loops, the field applies torque. This rotation turns a shaft and converts electrical energy into mechanical energy. A rectangular current-carrying loop with N turns in a uniform magnetic field has zero net force. Even so, it can still experience net torque. The torque depends on the current I,...

the hall effect

Hall Voltage and Charge Carriers

Hall voltage and charge carriers are explained through Edwin H. Hall’s 1879 experiment. His setup helped identify the polarity of the main charge carriers in a conducting material. It also showed, for the first time, that the charge carriers in most metals are negative. A metal slab is placed in a constant magnetic field. The electrons move from right to left, so the magnetic force pushes them toward the top edge of the slab. This leaves excess negative charge at the top and excess positive...

thomson's e/m experiment

Electron Speed Selector in Thomson’s Tube

A velocity selector uses electric and magnetic fields to choose charged particles with one speed from a beam. Many beams from a heated cathode contain particles moving at different speeds, so this setup helps produce a uniform beam. The electric and magnetic fields are perpendicular to the particle’s motion and to each other. In this arrangement, a particle with charge q, speed v, and mass m enters from the top. The magnetic field points into the plane of the paper, and the electric field...

key terms and concepts

Learn how magnetic poles attract and repel, how compasses work, and how magnetism powers motors, generators, MRI, and more in everyday life.

Magnetic Poles and Everyday Uses | JoVE K12

physics

JoVE Core - Fisica apresenta a teoria e a aplicação de tópicos fundamentais da física, incluindo cinemática, dinâmica, mecânica dos fluidos, estática, ondas e acústica, com vídeos animados concisos e de fácil compreensão. Além disso, os vídeos de cientistas em ação demonstram a aplicação de conceitos relacionados em experimentos de pesquisa clássica e original realizados nos laboratórios de todo o mundo hoje em dia.

PS.Phy.5.1

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Ohio’s Learning Standards and Model Curriculum

Electricity And Magnetism

Magnetic fields

Physical Geology

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Igneous, Metamorphic And Sedimentary Rocks

Sedimentary

Virginia  Standards of Learning

HIgh School

PS.9

PS.9.d

PH.7

PH.7.a

PH.7.b

Minnesota Academic Standards in Science

Chemistry

4.2.2 9C.3.2.2.1

3.1.1 9P.2.2.1.3

Arizona Science Standards

High School

HS.P2

HS.P2U1.5

Alabama Course of Study Science

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Waves and Their Applications in Technologies for Information Transfer

9-12.PS.2.3.a

Texas Essential Knowledge and Skills

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112.48.c.11.

112.48.c.11.D.

Florida Department of Education

SC.912.P.10

SC.912.P.10.16

Chemistry and Physics

IPC.6

IPC.6.B

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New York State Science Learning Standards

HS. Forces and Interactions

HS-PS2-5.

HS. Energy

HS-PS3-5.

Georgia Standards of Excellence

SPS10.

Electromagnetism

Position and Displacement

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Average Velocity

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Instantaneous Velocity - I

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average-and-instantaneous-velocity-vectors

Average and Instantaneous Velocity Vectors

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Acceleration Vectors

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Resistivity

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PS.PSc.6.2

Continuity Equation

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Boundary Conditions for Current Density

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Electrical Conductivity

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PS.PSc.6.3

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Magnetic Field Lines

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Magnetic Flux

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Motion Of A Charged Particle In A Magnetic Field

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Magnetic Force

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Magnetic Force On A Current-Carrying Conductor

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Magnetic Force On Current-Carrying Wires: Example

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Use models to explain magnetism in terms of domains, interactions of poles, and magnetic fields.

Analyze motion in terms of speed, velocity, acceleration, and momentum.

Magnetic Poles and Everyday Uses

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