Chapter 8Chapter 8Magnetism & Its UsesMagnetism & Its Uses

Sec 1: MagnetismSec 1: Magnetism►Over 2000 years ago Greeks first Over 2000 years ago Greeks first

discovered magnetism in a mineral they discovered magnetism in a mineral they called magnetic.called magnetic.

►MagnetismMagnetism—properties and —properties and interactions with magnetsinteractions with magnets

►Magnets attract metal objects.Magnets attract metal objects.

Magnetic Force Magnetic Force && Magnetic Magnetic FieldsFields

►Magnetic forceMagnetic force—the interaction —the interaction between magnets.between magnets. The strength of this force increases as The strength of this force increases as

magnets move closer together.magnets move closer together.

►Magnetic fieldMagnetic field—the area surrounding a —the area surrounding a magnet that exerts the magnetic force.magnet that exerts the magnetic force. Iron and other magnets react to the Iron and other magnets react to the

magnetic force when placed in the magnetic magnetic force when placed in the magnetic field.field.

Magnetic field can be represented by lines of Magnetic field can be represented by lines of force, or magnetic field lines.force, or magnetic field lines.

Magnetic field lines of a bar Magnetic field lines of a bar magnetmagnet

Magnetic PolesMagnetic Poles►Magnetic field lines are closest to Magnetic field lines are closest to

each other at the ends of the bar each other at the ends of the bar magnetmagnet

►These are These are magnetic polesmagnetic poles—where —where the magnetic force exerted by the the magnetic force exerted by the magnet is the strongest.magnet is the strongest.

►AllAll magnets have a north and south magnets have a north and south pole.pole. Bar magnet—poles are at opposite endsBar magnet—poles are at opposite ends Horseshoe magnet—the poles are the two Horseshoe magnet—the poles are the two

ends (like a bent bar magnet)ends (like a bent bar magnet)

Interacting MagnetsInteracting Magnets►Magnets either attract or repel each Magnets either attract or repel each

other.other.►When 2 north poles or 2 south poles When 2 north poles or 2 south poles

come close, you can feel a force come close, you can feel a force preventing the magnets from preventing the magnets from touching.touching.

►North poles always attract south poles.North poles always attract south poles.►When 2 magnets come close, their When 2 magnets come close, their

magnetic fields combine.magnetic fields combine.

A Compass NeedleA Compass Needle►A compass contains a needle (a small A compass contains a needle (a small

bar magnet) that is free to rotate.bar magnet) that is free to rotate.►When placed near a bar magnet, the When placed near a bar magnet, the

north pole of the needle will turn north pole of the needle will turn towards the south pole of the magnet.towards the south pole of the magnet.

►A compass needle will point towards A compass needle will point towards the North Pole of Earth.the North Pole of Earth.

►Earth acts as like a gigantic bar Earth acts as like a gigantic bar magnet, and its magnetic field extends magnet, and its magnetic field extends into space.into space.

Earth’s Magnetic Earth’s Magnetic PolesPoles

►The north pole of a magnet is the end The north pole of a magnet is the end of the magnet that points towards of the magnet that points towards geographic north.geographic north.

►The north pole of a magnet attracts a The north pole of a magnet attracts a south magnetic pole.south magnetic pole.

►Earth’s south magnetic pole is near Earth’s south magnetic pole is near the geographic north pole.the geographic north pole. It is located in Canada about 1500km It is located in Canada about 1500km

from the geographic north pole.from the geographic north pole.

Magnetic MaterialsMagnetic Materials►A magnet will not attract all metal A magnet will not attract all metal

objects.objects.►Only a few elements can be made into Only a few elements can be made into

permanent magnetspermanent magnets Iron, cobalt, & nickelIron, cobalt, & nickel

►Objects made from these metals are not Objects made from these metals are not always magnetic.always magnetic. Put an iron nail next to a refrigerator, let go, Put an iron nail next to a refrigerator, let go,

and it falls to the floor.and it falls to the floor.

►You can make these metals behave like You can make these metals behave like magnets temporarily.magnets temporarily.

Permanent MagnetsPermanent Magnets► Iron, cobalt, or nickel can be made into Iron, cobalt, or nickel can be made into

permanent magnets by placing them in a permanent magnets by placing them in a strong magnetic field.strong magnetic field.

►This creates a magnetic field inside the materialThis creates a magnetic field inside the material► It can retain magnetic properties for a long It can retain magnetic properties for a long

time.time.►Permanent magnets can lose their magnetism if Permanent magnets can lose their magnetism if

heated or dropped.heated or dropped.►When a magnet is broken, each piece still has a When a magnet is broken, each piece still has a

north and south pole!north and south pole! Even the smallest pieces of a magnet have a north Even the smallest pieces of a magnet have a north

and south pole.and south pole.

Sec 2: Electricity & Sec 2: Electricity & MagnetismMagnetism

►Electric currents cause magnetic Electric currents cause magnetic fields.fields.

►The magnetic field around a current-The magnetic field around a current-carrying wire forms a circular pattern carrying wire forms a circular pattern around the wire.around the wire.

►The strength of the field depends on The strength of the field depends on the amount of current flowing in the the amount of current flowing in the wire.wire.

ElectromagnetsElectromagnets►ElectromagnetElectromagnet—a —a

temporary magnet made temporary magnet made by placing a piece of iron by placing a piece of iron inside a current-carrying inside a current-carrying coil of wire.coil of wire. When current flows When current flows

through the loop of wire, through the loop of wire, magnetic field lines form magnetic field lines form around the wire.around the wire.

The more loops of wire, The more loops of wire, the stronger the magnetic the stronger the magnetic field.field.

Properties of Properties of ElectromagnetsElectromagnets

►Electromagnets are Electromagnets are temporarytemporary because they are because they are only magnetic when current only magnetic when current is flowing through the wire.is flowing through the wire.

►Electromagnets convert Electromagnets convert electrical energy into electrical energy into mechanical energy to do mechanical energy to do work.work.

Stereo SpeakersStereo Speakers►The mechanical energy produced from The mechanical energy produced from

an electromagnet vibrates parts of a an electromagnet vibrates parts of a speaker to produce sound.speaker to produce sound.

Electric MotorsElectric Motors►Electric motorElectric motor—a device that —a device that

changes electrical energy into changes electrical energy into mechanical energy.mechanical energy. Contains an electromagnet that is Contains an electromagnet that is

free to rotate between poles of a free to rotate between poles of a permanent magnet connected to permanent magnet connected to the battery.the battery.

When current flows through the When current flows through the electromagnet, a magnetic field is electromagnet, a magnetic field is produced in the coil.produced in the coil.