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Unit 3 Lesson 4 Magnets and Magnetism
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Unit 3 Lesson 4 Magnets and Magnetism
Stuck on You
What are some properties of magnets?
• The term magnet describes any material that
attracts iron or objects made of iron.
• Many magnets are made of iron, nickel, cobalt, or
mixtures of these metals.
• When you bring two magnets together, they exert
a push or pull on each other called a magnetic
force. Magnetic force is one of only three forces
in nature that can act at a distance—electrostatic
force and gravity are the other two.
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Unit 3 Lesson 4 Magnets and Magnetism
What are some properties of magnets?
• Magnetic force results from spinning electric
charges in the magnets. The force can either push
the magnets apart or pull them together.
• Two magnets can push each other apart because
of their ends, or magnetic poles.
• Every magnet has a north pole and a south pole.
If you place the north poles of two magnets
together, they will repel, or push away. If you
place the north pole and the south pole of two
magnets near each other, they will attract, or
come together.
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Unit 3 Lesson 4 Magnets and Magnetism
What are some properties of magnets?
• The area surrounding a magnet where magnetic
forces can be detected is called the magnetic
field.
• A magnetic object placed anywhere in the
magnetic field will be affected by the magnet.
• A magnet’s magnetic field is strongest near its
poles. The greater the distance from the poles,
the weaker the magnetic field.
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Unit 3 Lesson 4 Magnets and Magnetism
What are some properties of magnets?
• Magnetic field lines enter a magnet at the south
pole and exit at the north pole.
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Unit 3 Lesson 4 Magnets and Magnetism
When Everything Lines Up
What causes magnetism?
• Whether a material is magnetic or not depends on
the material’s atoms.
• As an electron moves in an atom, it makes, or
induces, a magnetic field. The electron will then
have a north and a south magnetic pole.
• In most atoms, such as copper and aluminum, the
magnetic fields of the individual electrons cancel
each other out. These materials are not magnetic.
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Unit 3 Lesson 4 Magnets and Magnetism
What causes magnetism?
• The magnetic fields of the electrons in iron, nickel,
and cobalt atoms do not completely cancel each
other out. As a result, atoms of these materials
have small magnetic fields. These materials are
magnetic.
• In materials such as iron, nickel, and cobalt,
groups of atoms form tiny areas called domains.
The north and south poles of the atoms in a
domain line up and make a strong magnetic field.
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Unit 3 Lesson 4 Magnets and Magnetism
What causes magnetism?
• The domains in an object determine whether the
object is magnetic. When a magnetic material is
placed in a magnetic field, most of the domains
point toward the same direction, forming a
magnetic field around the entire object.
• In other materials, there are no domains to line
up because the atoms have no magnetic fields.
These materials cannot become magnetized.
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Unit 3 Lesson 4 Magnets and Magnetism
What causes magnetism?
• Which image shows an object’s domains before
magnetization, and which shows the object’s
domains after magnetization?
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Unit 3 Lesson 4 Magnets and Magnetism
What are some types of magnets?
• Some materials, such as soft iron, can be made
into magnets temporarily when placed in a strong
magnetic field. The material’s domains line up,
and the material is magnetized.
• Permanent magnets are difficult to make, but they
keep their magnetic properties longer.
• A material that can be turned into a magnet is
called ferromagnetic. A ferromagnetic material
can be turned into a permanent magnet when
placed in a strong magnetic field.
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Unit 3 Lesson 4 Magnets and Magnetism
What are some types of magnets?
• An electromagnet is an iron core wrapped with
electrical wire. When an electric current is in the
wire, a magnetic field forms. When the current is
turned off, the magnetic field stops.
• The strength of an electromagnet depends on the
strength of the electric current.
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Unit 3 Lesson 4 Magnets and Magnetism
Polar Opposites
How is Earth like a giant magnet?
• Earth has a magnetic field. Earth also has a north
magnetic pole and a south magnetic pole.
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Unit 3 Lesson 4 Magnets and Magnetism
How is Earth like a giant magnet?
• Scientists now think that Earth’s inner structure
produces its magnetic field. Earth’s inner core is
made of solid metals. Earth’s outer core is made
of liquid iron and nickel, which are ferromagnetic.
• As Earth rotates, the liquid outer core moves.
Charged particles, including electrons, move in the
liquid and form a magnetic field. The constant
rotation keeps Earth magnetized.
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Unit 3 Lesson 4 Magnets and Magnetism
How is Earth like a giant magnet?
• Earth’s magnetic field is strongest near its poles,
which can attract other magnets, such as the
needle of a compass.
• The “north” pole of a magnet gets its name
because it points toward Earth’s geographic North
Pole. How can the north end of a compass point to
the north magnetic pole?
• A better term for the north pole of a magnet
would be a “north-seeking” pole. Using these
terms, the magnetic pole near Earth’s North Pole
is considered the south pole of a magnet.
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Unit 3 Lesson 4 Magnets and Magnetism
How is Earth like a giant magnet?
• Earth’s magnetic poles are not the same as Earth’s
geographic poles. The geographic poles mark the
ends of Earth’s axis. The geographic poles are
near, but not exactly at, the magnetic poles.
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Unit 3 Lesson 4 Magnets and Magnetism
What is an aurora?
• The beautiful displays of light that can be seen at
northern or southern latitudes are related to
Earth’s magnetic field.
• The sun ejects charged particles. When they reach
Earth, they are guided by its magnetic field. They
enter Earth’s upper atmosphere near the magnetic
poles. There, the charged particles interact with
atoms in the air, causing the atoms to emit visible
light.
• This glow is called an aurora.
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