Magnetism

E. Q. – What is magnetism and how does it affect our everyday lives?

What is a magnet?• The definition of a magnet is

anything that is surrounded by a magnetic field and attracts iron or steel particles to it.

• A magnetic field is the area around a magnet where magnetic force can be felt.

• All magnets have two poles, named the North Pole and the South Pole.

• All metals are not attracted to magnets—only iron and steel are attracted.

• Magnets can occur naturally or they can be man-made.

• Magnets can be permanent or just temporary. Some magnets can be turned on and off.

• The ancient Greeks discovered natural magnets in the area called Magnesia, and that’s how magnets got their name.

What causes magnetism?• Just as electricity is caused by

the movement of electrons, so is magnetism.

• Electrons moved from place to place causes electricity.

• Magnetism is caused by the spinning of electrons as they move.

• In the atoms of almost all elements, about half of the electrons spin clockwise and half spin counterclockwise.

• In the atoms of magnets, most of the electrons spin in one direction and makes the atoms have “poles.”

• This still doesn’t make a magnet because the atoms’ poles are all pointing in different directions.

Non-magnet

Magnet

• If the atoms can be shifted so that their poles point in the same direction, then a magnet is created.

What’s the biggest magnet?• The Earth itself is a

huge magnet. • The Earth’s magnetic

properties guide such migrating animals as birds, whales, and butterflies on yearly journeys.

• Compass needles are attracted to the Earth’s magnetic North Pole and helped explorers sail safely out of sight of land.

• The Earth’s magnetic poles and geographic poles are not exactly in the same place.

• Compass needles point to the magnetic North Pole, not the geographic North Pole.

Equator

Magnetic North PoleGeographic North Pole

What kinds of magnets are there? • There are natural magnets and man-made magnets.• There are temporary magnets and permanent magnets.

The rock in the picture is magnetite, which is a natural magnet. It is also permanent.

The electromagnet in this picture is man-made and also temporary. It only works when electric current flows through the coil.

Magnetic Fields• The magnetic field around a magnet is always

strongest at the poles of the magnet. • You can see the lines of force if you sprinkle iron filings

on a piece of paper on top of a magnet.

What affects a magnet’s strength?A permanent magnet can be weakened by --- hitting it dropping it heating it

An electromagnet can be strengthened by --- adding more nails to the iron core of the magnet wrapping more turns of wire into the coil increase the voltage of the electric source.

What happens when you break a magnet?

• A magnet always has two poles; North and South. • If you break a magnet in half, you get TWO magnets, each

having two poles; North and South.• No matter how small the magnets get there will always be

two poles; North and South!

The Rule of Magnetic Poles• This is also called Coulomb’s Law.• It says that opposite poles attract and like poles repel.

Can Electricity cause Magnetism? • When electricity flows through a coil of wire, it causes a magnetic field

around the wire.• Put the wire coil between two permanent magnets. • If the current changes direction, the poles of the magnet are reversed.• The commutator changes the direction of current in the wire so that the

coil keeps moving in a circle. • The rotating coil spins, changing electric energy to mechanical energy. • This is an electric motor.

Can Magnetism cause Electricity?• Moving a magnet through the middle of a coil of wire or

moving the coil through a magnetic field makes electricity to flow through the wire.

• This is an electric generator, which changes mechanical energy to electrical energy.

Uses of Magnetism?• Magnetism makes lots of modern conveniences possible:• Electric generators• Electric motors• Stereo speakers• Telephones• Tape recorders• Junkyard electromagnets• Latches on refrigerator doors• Transformers• Many many more!