Lesson IV “Magnets & Magnetic Fields” Matter & Energy

S.W.B.A.T. Identify the effects of magnetic forces and how magnetic poles interact Identify the effects of magnetic forces and how magnetic poles interact Describe magnetic field lines around a magnet Describe magnetic field lines around a magnet Explain how & why materials become magnetized Explain how & why materials become magnetized

Magnetic Forces Ancient cultures recognized that some rocks contained “mysterious” particles that attracted iron Ancient cultures recognized that some rocks contained “mysterious” particles that attracted iron The word “magnet” originates from the ancient Greek city of Magnesia The word “magnet” originates from the ancient Greek city of Magnesia

Magnetic Forces Magnesia contained mineral deposits later called magnetite or lodestone Magnesia contained mineral deposits later called magnetite or lodestone The Chinese were the first to use magnetite to eventually make a compass needle for navigation The Chinese were the first to use magnetite to eventually make a compass needle for navigation

Magnetic Forces Magnetic force is an area of influence that attracts or repels other magnets, iron and other metals, or electric charges Magnetic force is an area of influence that attracts or repels other magnets, iron and other metals, or electric charges Magnetic force strength decreases with distance like the electric force Magnetic force strength decreases with distance like the electric force

Magnetic Forces Magnetic poles include a “north” and “south” point at the end of the magnet Magnetic poles include a “north” and “south” point at the end of the magnet Opposite poles (N)(S) attract Opposite poles (N)(S) attract Like poles (N)(N) & (S)(S) repel Like poles (N)(N) & (S)(S) repel

Like Poles Repel – Unlike Poles Attract

Magnetic Forces A magnetic field describes the area around the poles A magnetic field describes the area around the poles Lines are used showing field direction and strength as measured by a compass Lines are used showing field direction and strength as measured by a compass

Magnetic Forces Magnetic field lines start from the north and are strongest at the poles Magnetic field lines start from the north and are strongest at the poles Iron filings can also be used to “map out” magnetic field lines Iron filings can also be used to “map out” magnetic field lines Iron filings show where magnetic forces are strongest & weakest Iron filings show where magnetic forces are strongest & weakest

Magnetic Forces Earth’s magnetosphere is generated from the iron core rotating slightly faster than the mantle Earth’s magnetosphere is generated from the iron core rotating slightly faster than the mantle The magnetic field extends (on average) about ½ way to the Moon and protects Earth from harmful cosmic radiation The magnetic field extends (on average) about ½ way to the Moon and protects Earth from harmful cosmic radiation

Magnetic Forces Geographic north is located 90 degrees north of the equator Geographic north is located 90 degrees north of the equator Magnetic north is located about 81 degrees north of the equator Magnetic north is located about 81 degrees north of the equator Earth’s magnetic field “wanders” or moves due to changes in iron core currents and mantle interactions Earth’s magnetic field “wanders” or moves due to changes in iron core currents and mantle interactions

Video (1:58) “Magnetic North Pole Video (1:58) “Magnetic North Pole Moves to Siberia Moves to SiberiaMoves to Siberia Moves to Siberia”

Magnetic Forces Magnetic north is actually magnetic south - since the north tip of a magnet is attracted to it and opposites attract! Magnetic north is actually magnetic south - since the north tip of a magnet is attracted to it and opposites attract! Magnetic poles on Earth have switched places many times in the past Magnetic poles on Earth have switched places many times in the past

Magnetic Materials Atoms have electrons that “spin” – which gives the electrons magnetic properties Atoms have electrons that “spin” – which gives the electrons magnetic properties “Paired” electrons spin opposite to each other which cancels out their magnetic properties “Paired” electrons spin opposite to each other which cancels out their magnetic properties

Magnetic Materials Unpaired electrons in metals such as iron, nickel & cobalt can form a strong magnetic field Unpaired electrons in metals such as iron, nickel & cobalt can form a strong magnetic field Magnetic domain refers to a region with a very large number of unpaired electrons Magnetic domain refers to a region with a very large number of unpaired electrons

Magnetic Materials Ferromagnetic metals like iron can become magnetized only because of its magnetic domains Ferromagnetic metals like iron can become magnetized only because of its magnetic domains Ferromagnetic materials can be temporarily magnetized if placed in a magnetic field Ferromagnetic materials can be temporarily magnetized if placed in a magnetic field The magnetic domains “line up” or align to create a temporary magnet The magnetic domains “line up” or align to create a temporary magnet

Magnetic Materials Temporary magnets quickly lose their magnetism after leaving a magnetic field Temporary magnets quickly lose their magnetism after leaving a magnetic field A permanent magnet holds on to its magnetic properties after leaving a magnetic field A permanent magnet holds on to its magnetic properties after leaving a magnetic field

Magnetic Materials Cutting a magnet in half will create two separate magnets, each with a north & south pole Cutting a magnet in half will create two separate magnets, each with a north & south pole A magnet cannot have just one pole – no matter how many times you cut it in half! A magnet cannot have just one pole – no matter how many times you cut it in half!

Magnetic Materials Super magnets are the strongest type of permanent magnets Super magnets are the strongest type of permanent magnets Super magnets are used in many applications such as MRI’s and particle accelerators Super magnets are used in many applications such as MRI’s and particle accelerators Video (3:32) “Largest Neodymium Magnet Video (3:32) “Largest Neodymium Magnet in the World? ” in the World? ”

Class Activity A magnet is placed on a refrigerator door to hold up your A+ assignment given in science class A magnet is placed on a refrigerator door to hold up your A+ assignment given in science class Explain which material is the permanent magnet and which is the temporary magnet and why Explain which material is the permanent magnet and which is the temporary magnet and why