lesson iv “magnets & magnetic fields”
DESCRIPTION
Lesson IV “Magnets & Magnetic Fields”. Matter & Energy. S.W.B.A.T. Identify the effects of magnetic forces and how magnetic poles interact Describe magnetic field lines around a magnet Explain how & why materials become magnetized. Magnetic Forces. - PowerPoint PPT PresentationTRANSCRIPT
Lesson IV “Magnets & Magnetic Fields”
Matter & Energy
S.W.B.A.T.
• Identify the effects of magnetic forces and how magnetic poles interact
• Describe magnetic field lines around a magnet
• Explain how & why materials become magnetized
Magnetic Forces• Ancient cultures
recognized that some rocks contained “mysterious” particles that attracted iron
• The word “magnet” originates from the ancient Greek city of Magnesia
Magnetic Forces
• 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
Magnetic Forces• 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 Forces• Magnetic poles include
a “north” and “south” point at the end of the magnet
• Opposite poles (N)(S) attract
• Like poles (N)(N) & (S)(S) repel
Like Poles Repel – Unlike Poles Attract
Magnetic Forces• A magnetic field describes the area
around the poles• 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• Iron filings can also be used to “map
out” magnetic field lines• 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
• 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• 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
Video (1:58) “Magnetic North Pole 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 poles on Earth have switched places many times in the past
Magnetic Materials• Atoms have electrons that “spin” –
which gives the electrons 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
• 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 materials can be temporarily magnetized if placed in a magnetic field
• 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
• 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
• 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 used in many applications such as MRI’s and particle accelerators
Video (3:32) “Largest Neodymium Magnet in the World?”
Class Activity
• 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