What is Magnetism?Text pages 654 to 659

Key conceptsWhat are the properties of a magnet?

How do magnetic poles interact?What is the shape of a magnetic field?

What is Magnetism?• Natural magnetism is a property of some iron-rich

materials.

• Magnetite is named for the ancient Greek city of Magnesia (now in Turkey) in Asia Minor, which had many deposits of magnetite.

• Rocks containing magnetite attracted materials made of iron– The Chinese used the properties of magnets to make the first

compasses, which were a big help in development for navigation and exploration.

Properties of Magnets

•A magnet is any material that

attracts iron and materials that

contain iron

•Magnets attract or repel other

magnets

•One part of a magnet will always

point north when allowed to swing

freely

Magnetic Poles• Magnets have a pole on each end. One side is the North Pole

while the other is the South Pole.

• The end of magnetic pole that swings towards the north pole when it is allowed to swing freely is called the north end of the magnet

• If you break a bar magnet in half you don’t destroy the magnet but actually make TWO magnets.– It is impossible to have a magnet with one pole.

What is a Magnetic Field?• Magnetic field is the force surrounding a magnetic object.

– This force can push or pull other objects without touching them.

• Around the North Pole the magnetic field lines curve outward

• Around the South Pole the magnetic field lines curve inward.

• The magnetic field is stronger the closer you are to the magnet itself, and is even stronger at the poles.

Magnetic PolesMagnetic poles that are unlike attract each other, and magnetic poles that are alike repel each other.

What you may not know is: like poles repel while opposite poles attract because of the way the field lines are moving in a magnet.Magnetic Field Lines exit from the north end and enter at the south end of a magnet

Magnetic PolesWhen two like poles interact, they act like bumper cars at a fair, the bump up against each other and push the magnets away from each other

Magnetic PolesWhen two unlike poles interact, they pull each other closer

Inside a MagnetText Pages 662 to 667

Key Concepts:•How can an atom behave like a magnet?•How are magnetic domains arranged in a magnetic material?•How can magnets be changed?

The Atom

Magnetic properties depend on the structure of atomsRemember:

Protons have positive chargeElectrons have negative charge

Each electron has a property called electron spinA spinning electron produces a magnetic field that makes the electron behave like a tiny magnet in an atom

Most atoms have pairs of electrons that spin in opposite directions…this produces magnetic fields that cancel each other out.

Some atoms have electrons that are not paired, these atoms tend to have strong magnetic properties.

- These are the materials that are made into magnets

What Makes a Magnet?• Non-magnetized objects have their magnetic domains

randomly pointing in all directions. – Magnetic domains are a group of atoms that have their magnetic

poles pointing in the same direction.

• Materials that can become magnetized easier have many magnetic domains that can be re-arranged quickly when a magnetized object is brought close to it.

* Cool Fact *

• Inventors in Egypt 2000 years ago used magnetite to make statues float in midair. The statue was carved out of magnetite. Pieces of magnetite in the floor, walls, and ceiling could keep the statue suspended in air.

Magnetic Materials• Ferromagnetic Materials- materials that show

strong magnetic properties (its magnetic domains are aligned)

– Examples in nature: iron, nickel, cobalt, and gadolinium

• Alloy magnets- made from several different materials Alnico (Aluminum, nickel, iron, cobalt)

• Ferrite magnets- mixture of substances that contain ferromagnetic elements Stronger and less expensive than metal magnets

• Neodymium magnets – made from rare elements. Extremely strong magnets

Magnetic Materials

Making and Changing Magnets

• 2 ways to make magnets– Place unmagnetized ferromagnetic material in the

presence of a strong magnetic field– Rubbing ferromagnetic materials with one pole of

a magnet

• Temporary magnet- – easy to magnetize, but easily loses its

magnetism

• Permanent magnet- – hard to magnetize, but keeps its magnetism for

a long period of time

Making and Changing Magnets

2 Ways to destroy a magnet

• Drop or strike a magnet hard

• Heat a magnet

Breaking Magnets

When you break a magnet in twoYou don’t end up with a magnet with a north pole in one hand and the south pole in the other hand

You have two smaller magnets!

Both new magnets each have a north and south pole

Magnetic Earth

Text pages 670 to 675

Key Concepts:•How is Earth like a bar magnet?•What are the effects of Earth’s magnetic field?

Earth as a Magnet

1500’s Sir William Gilbert hypothesized that a compass behaves like it does because Earth is a giant magnet…..other scientists laughed at this idea

Well….He had the last laugh…he was right!

Just like a bar magnet, Earth has a magnetic field surrounding it and two magnetic poles

Compasses• A compass is a magnetic needle that is free to turn and

align itself along the magnetic field lines of Earth or the nearest strongest magnet.

• The compass needle point labeled “north” points to Earth’s North Pole. Actually, if the north end of the magnet points to the Geographic North pole---what pole of Earth’s magnetic field must the compass point?

• Animals have natural organic compasses in the brains that they use to navigate themselves around. This natural they have in their brains is a very tiny piece of magnetite that acts as a compass and tells them which direction they are going.

Earth as a Magnet

The Earth's magnetic field appears to come from a giant bar magnet, but with its south pole located up near the Earth's north pole (near Canada).

The magnetic field lines come out of the Earth near Antarctica and enter near Canada.

The geographic poles do not line up with the magnetic poles…

Geographic North Pole is near the Magnetic South Pole

Geographic South Pole is near the Magnetic North Pole

Hey! That must be why a compass’ needle always points

north…the magnet’s north pole points to the Earth’s Magnetic

South Pole (which is really the Earth’s geographic North Pole!!)

Earth’s Magnetic Field

• Earth is one big magnet that we live on day in and day out.

• The cause of Earth’s magnetic field is actually not known, but scientists strongly suspect it is due to the liquid metals moving in the core.

• Earth’s magnetic field is called the magnetosphere.– The magnetosphere is responsible for protecting us from the very

harmful particles ejected by the sun’s surface in the form of the solar wind.

– It deflects like a shield the particles so that they curve away from the planet and don’t enter out atmosphere to harm the living tissue in animals, plants, and us.

Earth’s Magnetic Field

• Earth also has a magnetic field around it that extends into space. It is called the magnetosphere. Scientists do not know how its magnetic field is produced but they have a good idea that it could be from the liquid metal moving around in the core.

• Without the Earth’s magnetic field the sun’s energy from solar bursts would reach the surface where we live and make it nearly impossible for anything to live because of the high amounts of radiation.

The Magnetosphere

Earth’s magnet field affects the movements of electrically charged particles in space

•1,000 to 25,000 km above earth’s surface are two doughnut shaped regions called the Van Allen Belts•Contain electrons and protons traveling at a very high speed•Shaped by the “solar wind”•Highly charged particles flowing from the sun

Auroras

High speed, charged particles in the solar wind get close to Earth, they interact with atoms in the higher reaches of Earth’s atmosphere.•Some atoms will then give off light•Produces a curtain of shimmering light in the sky•Called an Aurora•Occurs from 60 to 90 degrees latitude•Northern Lights (Aurora Borealis)•Southern Lights (Aurora Australis)