Magnets and Magnetism

• Did you know? More than 2000 years Did you know? More than 2000 years ago, the Greeks discovered a mineral that ago, the Greeks discovered a mineral that attracted objects containing iron. attracted objects containing iron. Because this mineral was found in a part Because this mineral was found in a part of Turkey called Magnesia, the Greeks of Turkey called Magnesia, the Greeks called it Magnetite. Today called it Magnetite. Today anyany material material that attracts iron is called a magnet.that attracts iron is called a magnet.

Magnets and Magnetism

• The magnetic effects of a magnet The magnetic effects of a magnet are NOT evenly distributed through are NOT evenly distributed through the magnet.the magnet.

• The parts of a magnet where The parts of a magnet where the magnetic effects are the magnetic effects are strongest are called the poles.strongest are called the poles.

Magnets and Magnetism• If you attach a magnet to a string If you attach a magnet to a string

so that the magnet is free to so that the magnet is free to rotate, you will see that one end of rotate, you will see that one end of the magnet always ends up the magnet always ends up pointing north and the other end pointing north and the other end will point to the south.will point to the south.

• Magnetic poles always occur in Magnetic poles always occur in pairs, you will never find a pairs, you will never find a magnet with only a north pole magnet with only a north pole or only a south pole.or only a south pole.

Magnets and Magnetism• The force of The force of

attraction or attraction or repulsion between repulsion between the poles of the poles of magnets is called magnets is called the magnetic force.the magnetic force.

• The magnetic force The magnetic force depends on how the depends on how the poles of the magnets poles of the magnets line up.line up.

Magnets and Magnetism

• A magnetic field A magnetic field exists in the exists in the region around a region around a magnet in which magnet in which magnetic forces magnetic forces can act.can act.

Magnets and Magnetism

• Magnetic field lines are close Magnetic field lines are close together where the magnetic force together where the magnetic force is strongest, and is strongest, and

farther away farther away where the where the force is weaker.force is weaker.

Magnets and Magnetism

• Some materials are magnetic, and Some materials are magnetic, and some are not. What causes the some are not. What causes the difference? difference?

• Whether a material is magnetic Whether a material is magnetic depends on the atoms in the depends on the atoms in the material.material.

Magnets and Magnetism

• All matter is composed of atoms that All matter is composed of atoms that include protons, electrons and neutrons. include protons, electrons and neutrons. Moving electrons produce magnetic Moving electrons produce magnetic fields that can give an atom a north and fields that can give an atom a north and a south pole.a south pole.

• In most materials, the magnetic fields of In most materials, the magnetic fields of individual atoms cancel each other out. individual atoms cancel each other out.

Magnets and Magnetism• But in some But in some

materials, materials, the the atoms in a atoms in a magneticmagnetic domaindomain are arranged so are arranged so that the north and that the north and south poles of all south poles of all the atoms line up the atoms line up and create a strong and create a strong magnetic field.magnetic field.

Magnets and MagnetismTypes of magnets:Types of magnets:Ferromagnets – magnets made with metalsFerromagnets – magnets made with metalsElectromagnets – produced by an electric Electromagnets – produced by an electric

current.current.Temporary magnets – made from materials Temporary magnets – made from materials

that are easy to magnetize, but they that are easy to magnetize, but they lose their magnetization easily too.lose their magnetization easily too.

Permanent magnets – difficult to Permanent magnets – difficult to magnetize, but retain their magnetic magnetize, but retain their magnetic properties better.properties better.

Magnets and Magnetism

Did you know? Did you know? In 1600, English In 1600, English

physician William physician William Gilbert suggested Gilbert suggested that magnets that magnets point to the north point to the north because Earth because Earth itself is one GIANT itself is one GIANT magnet.magnet.

Magnets and Magnetism

• Although you can Although you can thinkthink of Earth as of Earth as have a giant bar magnet in the have a giant bar magnet in the center, there really isn’t a magnet center, there really isn’t a magnet there.there.

• The temperature of Earth’s core is The temperature of Earth’s core is so high that atoms in it move too so high that atoms in it move too violently to remain in domains.violently to remain in domains.

Magnets and Magnetism

• Earth’s Earth’s magnetic field is magnetic field is produced by the produced by the movement of movement of charges in the charges in the Earth’s core.Earth’s core.

Magnets and Magnetism

• One of the most spectacular effects One of the most spectacular effects caused by the Earth’s magnetic caused by the Earth’s magnetic field is a curtain of light calledfield is a curtain of light called an an aurora.aurora.

Magnets and MagnetismMagnets and Magnetism

• An aurora is formed when charged An aurora is formed when charged particles from the sun interact with particles from the sun interact with atoms in Earth’s atmosphere.atoms in Earth’s atmosphere. We see We see the interactions at Earth’s magnetic the interactions at Earth’s magnetic field.field.