Section 1: Magnets And Magnetic Fields

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MagnetismSection 1Section 1: Magnets and Magnetic FieldsPreview Key Ideas Bellringer Magnets Magnetic Fields Earth’s Magnetic Field

MagnetismSection 1Key Ideas〉What happens when the poles of two magnetsare brought close together?〉What causes a magnet to attract or repelanother magnet?〉How is Earth’s magnetic field oriented?

MagnetismSection 1Bellringer1. Most of us use magnets in our daily life withoutthinking about it. Name five places that you usemagnets.2. If you had two bar magnets and you touched the endof one bar magnet to the end of the other bar magnet,what are the two possible outcomes? If you rotatedone of the bar magnets 180 , what are the twopossible outcomes?3. Explain why a compass is a useful tool for navigation.

MagnetismSection 1Bellringer, continued4. On Earth, there is the magnetic N pole and thegeographic North Pole. According to the pictureabove, are they located at the same geographiclocation? Where do you think the magnetic S poleis located?

MagnetismSection 1Magnets〉What happens when the poles of two magnetsare brought close together?〉Two like poles repel each other. Two unlikepoles attract each other. magnetic pole: one of two points, such as the ends ofa magnet, that have opposing magnetic qualities– All magnets have at least one pair of poles, a northpole and a south pole.– It is impossible to isolate a magnet’s south pole fromthe magnet’s north pole.

MagnetismSection 1Magnets, continued Some materials can be made into permanent magnets. A magnetized piece of iron is called a “permanent”magnet, but its magnetism can be weakened oreven removed. Iron is a soft magnetic material. It is easily magnetized. It tends to lose its magnetic properties easily. Cobalt is a hard magnetic material. It more difficult to magnetize. Once magnetized, it doesn’t lose its magnetismeasily.

MagnetismSection 1Magnetic Fields〉What causes a magnet to attract or repelanother magnet?〉Magnets repel or attract each other becauseof the interaction of their magnetic fields. magnetic field: a region where a magnetic force canbe detected

MagnetismSection 1Magnetic Fields, continued Magnets are sources of magnetic fields. Moving charges create magnetic fields. magnetic domains: groups of atoms that all line upthe same way and form small, magnetized regionswithin a material Magnetic field lines are used to represent a magneticfield.– Field lines always form closed loops. The magnetic field gets weaker with distance fromthe magnet.

MagnetismSection 1Magnetic Fields, continued Magnetic field lines that areclose together indicate astrong magnetic field. Field lines that are fartherapart indicate a weaker field. Magnetic field lines begin atthe north pole of a magnet andend at the south pole of themagnet.

MagnetismSection 1Magnetic Fields, continued Compasses align with Earth’s magnetic field.– The compass points in the direction that lies alongthe magnetic field line at a given point.– By convention, the pole of a magnet that pointsnorth is painted red.

MagnetismSection 1Earth’s Magnetic Field〉How is Earth’s magnetic field oriented?〉Earth’s magnetic field lines run fromgeographic south to geographic north. The pole in Antarctica is a magnetic north pole. The pole in northern Canada is a magnetic south pole.

MagnetismSection 1Earth’s Magnetic Field, continued Earth’s magnetic field has both direction and strength. The source of Earth’s magnetism is not yet fullyunderstood.– The iron in the core is too hot to retain anymagnetic properties.– The circulation of ions or electrons in the liquidlayer of Earth’s core may be the source of themagnetism. The sun also has a magnetic field and ejects chargedparticles into space.

MagnetismSection 2Section 2: Magnetism from Electric CurrentsPreview Key Ideas Bellringer Electromagnetism Electromagnetic Devices

MagnetismSection 2Key Ideas〉What happens to a compass near a wire thatis carrying a current?〉Why are electric motors useful?

MagnetismSection 2BellringerThe temporary magnetic field created by current flowingthrough a wire is used in many small appliances.1. List as many things as possible that contain a smallelectric motor.2. What keeps the coil in an electric motor spinning?3. A sewing machine needle can be magnetized bygently stroking it with a magnet in one direction.What is a possible explanation for this?

MagnetismSection 2Electromagnetism〉What happens to a compass near a wire that iscarrying a current?〉When the wire carries a strong, steady current,all of the compass needles move to align withthe magnetic field created by the electric current. Hans Christian Oersted found that magnetism isproduced by moving electric charges.– Electric currents produce magnetic fields.

MagnetismSection 2Electromagnetism, continued Use the right-hand rule to find the direction of themagnetic field produced by a current. right-hand rule:– If you hold a wire in your right hand and point yourthumb in the direction of the positive current, thedirection that your fingers curl is the direction of themagnetic field.

MagnetismSection 2The Right-Hand Rule The thumb points in thedirection of the current. The fingertips point inthe direction of themagnetic field. The magnetic field runscounterclockwise.

MagnetismSection 2Magnetic Field of a Current-CarryingWire

MagnetismSection 2Electromagnetism, continued Solenoids and bar magnets have similar magnetic fields. solenoid: a coil of wire with an electric current in it– In a solenoid, the magnetic field of each loop of wireadds to the strength of the magnetic field of anyneighboring loops. The strength of a solenoid can be increased.– More loops or more current can create a strongermagnetic field. electromagnet: a coil that has a soft iron core and thatacts as a magnet when an electric current is in the coil– The magnetic field of the rod adds to the coil’s field.

MagnetismSection 2Electromagnetism, continued Moving charges cause magnetism.– Negatively charged electrons moving around thenuclei of atoms make magnetic fields.– Atomic nuclei also have magnetic fields becauseprotons move within the nucleus.– Each electron has a property called electron spin,which also produces a tiny magnetic field. The magnetism of the uncanceled fields in certainmaterials combines to make the materials magneticoverall.

MagnetismSection 2Electromagnetic Devices〉Why are electric motors useful?〉A motor can perform mechanical work when it isattached to an external device. electric motor: a device that converts electrical energy tomechanical energy Galvanometers detect current.– galvanometer: an instrument that detects, measures,and determines the direction of a small electric current

MagnetismSection 2Electromagnetic Devices, continued ammeter: measures current voltmeter: measures voltage. Motors use a commutator to spin in one direction.– commutator: a device used to make the currentchange direction every time the flat coil makes a halfrevolution.– brushes: devices that connect the wires to thecommutator

MagnetismElectric MotorSection 2

MagnetismSection 3Section 3: Electric Currents from MagnetismPreview Key Ideas Bellringer Electromagnetic Induction The Electromagnetic Force Transformers

MagnetismSection 3Key Ideas〉What happens when a magnet is moved into orout of a coil of wire?〉How are electricity and magnetism related?〉What are the basic components of atransformer?

MagnetismSection 3Bellringer1. List as many items as you can that use DC current.(Hint: Batteries supply DC current.)2. List as many items as you can that use AC current.(Hint: Standard wall outlets supply AC current.)3. If you want to plug a CD player that normally usesbatteries into a wall socket, an AC adapter isrequired. What is the function of the AC adapter?4. Electric power that goes into a neighborhood must bestepped down, or decreased, in voltage before itgoes into a home. Explain why this is necessary.

MagnetismSection 3Electromagnetic Induction〉What happens when a magnet is moved intoor out of a coil of wire?〉Moving a magnet into and out of a coil of wirecauses charges in the wire to move. electromagnetic induction: the process of creatinga current in a circuit by changing a magnetic field Faraday’s law states:An electric current can be produced in a circuitby a changing magnetic field crossing the circuit.

MagnetismSection 3Electromagnetic Induction, continued As the loop moves in and out of the magnetic field ofthe magnet, a current is induced in the circuit. Rotating the circuit or changing the strength of themagnetic field will also induce a current in the circuit. Electromagnetic induction obeys conservation ofenergy.– Pushing a loop through a magnetic field requireswork.

MagnetismSection 3Electromagnetic Induction, continued

MagnetismSection 3Electromagnetic Induction, continued The magnetic force acts on moving electric charges.– The force is at its maximum value when thecharge moves perpendicularly to the field.– As the angle between the charge’s direction andthe direction of the magnetic field decreases, theforce on the charge decreases. The magnetic force acts on wires carrying a current.

MagnetismSection 3Electromagnetic Induction, continued

MagnetismSection 3Electromagnetic Induction, continued Generators convert mechanical energy into electricalenergy. generator: a machine that converts mechanicalenergy to electrical energy alternating current (AC): an electric current thatchanges direction at regular intervals– For each half rotation of the loop, the currentproduced by the generator reverses direction. AC generators produce the electrical energy you usein your home.

MagnetismAC GeneratorSection 3

MagnetismInduced CurrentSection 3

MagnetismSection 3The Electromagnetic Force〉How are electricity and magnetism related?〉Electricity and magnetism are two aspects of asingle force, the electromagnetic force. The energy that results from these two forces is calledelectromagnetic (EM) energy. Light is a form of electromagnetic energy. EM waves are made up of oscillating electric andmagnetic fields that are perpendicular to each other.

MagnetismSection 3Transformers〉 What are the basic components of a transformer?〉In its simplest form, a transformer consists oftwo coils of wire wrapped around oppositesides of a closed iron loop. transformer: a device that increases or decreasesthe voltage of alternating current primary coil: wire attached to a source of alternatingcurrent secondary circuit: wire attached to an appliance

MagnetismSection 3Transformers, continued Current in the primary coil creates a changingmagnetic field that magnetizes the iron core. The changing magnetic field of the iron core theninduces a current in the secondary coil. Transformers can increase or decrease voltage.– The voltage induced in the secondary coil of atransformer depends on the number of loops, orturns, in the coil.

MagnetismSection 3Transformers, continued In a step-up transformer, the primary coil has fewerturns than the secondary coil does.– The voltage across the secondary coil is greaterthan the voltage across the primary coil. In a step-down transformer, the secondary coil hasfewer loops than the primary coil does.– The voltage across the secondary coil is lower thanthe voltage across the primary coil.

MagnetismSection 3Transformers, continued Transformers must obey the law of conservation ofenergy.– The current in the secondary coil of a step-uptransformer is always less than the current in theprimary coil. Transformers are used in the transfer of electricalenergy.

MagnetismTransformers, continuedSection 3

Aug 11, 2015 · Magnetic field lines are used to represent a magnetic field. –Field lines always form closed loops. The magnetic field gets weaker with distance from the magnet. Magnetism Section 1 Magnetic Fields,

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