Transcript magnetic field

Chapter 16
Electromagnetism
Preview
Section 1 Magnets and Magnetism
Section 2 Magnetism from Electricity
Section 3 Electricity from Magnetism
Concept Mapping
Chapter 16
Section 1 Magnets and Magnetism
Bellringer
Given the following objects, a piece of aluminum foil, a
nickel, a plastic figure, a piece of wood, a glass vase,
and some paper clips, predict which objects will be
attracted to a magnet. How do you know?
Record your answers in your science journal.
Chapter 16
Section 1 Magnets and Magnetism
Objectives
• Describe the properties of magnets.
• Explain why some materials are magnetic and some
are not.
• Describe four kinds of magnets.
• Give two examples of the effect of Earth’s magnetic
field.
Chapter 16
Section 1 Magnets and Magnetism
Properties of Magnets
• Magnetic Poles are points on a magnet that have
opposite magnetic qualities.
• North and South The pole of a magnet that points
to the north is called the magnet’s north pole. The
opposite end of the magnet, called the south pole,
points to the south.
Chapter 16
Section 1 Magnets and Magnetism
Properties of Magnets, continued
• Magnetic Forces When you bring two magnets
close together, the magnets each exert a magnetic
force on the other. These magnetic forces result from
spinning electric charges in the magnets. The force
can either push the magnets apart of pull them
together.
Chapter 16
Section 1 Magnets and Magnetism
Chapter 16
Section 1 Magnets and Magnetism
Properties of Magnets, continued
• Magnetic Fields A magnetic field exists in the region
around a magnet in which magnetic forces can act.
Chapter 16
Section 1 Magnets and Magnetism
The Cause of Magnetism
• Atoms and Domains In materials such as iron,
nickel, and cobalt, groups of atoms are in tiny areas
called domains. The north and south poles of the
atoms in a domain line up and make a strong
magnetic field.
Chapter 16
Section 1 Magnets and Magnetism
The Cause of Magnetism, continued
• Losing Alignment When domains move, the
magnet is demagnetized, or loses its magnetic
properties.
• Making Magnets You can make a magnet from
demagnetized material if you line up its domains with
another magnet.
Chapter 16
Section 1 Magnets and Magnetism
The Cause of Magnetism, continued
• Cutting a Magnet When you cut a magnet in half,
you end up with two magnets.
Chapter 16
Section 1 Magnets and Magnetism
Kinds of Magnets
• Atoms and Domains Some magnets, called
ferromagnets, are made of iron, nickel, cobalt, or
mixtures of those metals. Another kind of magnet is the
electromagnet. This is a magnet made by an electric
current.
• Temporary and Permanent Magnets Temporary
magnets are made from materials that are easy to
magnetize. But they tend to lose their magnetization
easily. Permanent magnets are difficult to magnetize,
but tend to keep their magnetic properties longer.
Chapter 16
Section 1 Magnets and Magnetism
Earth as a Magnet
• One Giant Magnet Earth behaves as if it has a bar
magnet running through its center.
• Poles of a Compass Needle The point of a
compass needle is attracted to the south pole of a
magnet. Opposite poles of magnets attract each other.
• South Magnetic Pole near North Geographic Pole
A compass needle points north because the magnetic
pole of Earth that is closest to the geographic North
Pole is a magnetic south pole.
Chapter 16
Section 1 Magnets and Magnetism
Chapter 16
Section 1 Magnets and Magnetism
Earth as a Magnet, continued
• The Core of the Matter Scientists think that the
Earth’s magnetic field is made by the movement of
electric charges in the Earth’s core.
• A Magnetic Light Show Earth’s magnetic field plays
a part in making auroras. An aurora is formed when
charged particles from the sun hit oxygen and nitrogen
atoms in the air.
Chapter 16
Section 1 Magnets and Magnetism
Earth’s Magnetic Field
Click below to watch the Visual Concept.
Visual Concept
Chapter 16
Section 2 Magnetism from Electricity
Bellringer
Suppose you had a machine that could levitate heavy
objects with the flick of a switch. Write a paragraph in
your science journal about how this machine would
make your life easier.
Chapter 16
Section 2 Magnetism from Electricity
Objectives
• Identify the relationship between an electric current
and a magnetic field.
• Compare solenoids and electromagnets.
• Describe how electromagnetism is involved in the
operation of doorbells, electric motors, and
galvanometers.
Chapter 16
Section 2 Magnetism from Electricity
The Discovery of Electromagnetism
• Hans Christian Oersted Danish physicist Hans
Christian Oersted discovered the relationship between
electricity and magnetism in 1820.
• More Research From his experiments, Oersted
concluded that an electric current produces a magnetic
field. His research was the first research in
electromagnetism—the interaction between electricity
and magnetism.
Chapter 16
Section 2 Magnetism from Electricity
Chapter 16
Section 2 Magnetism from Electricity
Using Electromagnetism
• A solenoid is a coil of wire that produces a magnetic
field when carrying an electric current.
• An electromagnet is made up of a solenoid wrapped
around an iron core.
• Turning Electromagnets On and Off
Electromagnets are very useful because they can be
turned on and off as needed. The solenoid has a field
only when there is electric current in it.
Chapter 16
Section 2 Magnetism from Electricity
Applications of Electromagnetism
• Doorbells Two solenoids in a doorbell allow the
doorbell to work.
• Magnetic Force and Electric Current An electric
current can cause a compass needle to move. The
needle is a small magnet. This property is useful in
electric motors.
Chapter 16
Section 2 Magnetism from Electricity
Applications of Electromagnetism, continued
• An electric motor is a device that changes electrical
energy into mechanical energy. All electric motors have
an armature—a loop or coil of wire that can rotate.
• Galvanometers A galvanometer measures current. A
galvanometer has an electromagnet placed between
the poles of a permanent magnet.
Chapter 16
Section 2 Magnetism from Electricity
Chapter 16
Section 3 Electricity from Magnetism
Bellringer
Have you ever discovered something by accident?
Maybe you looked in a dictionary for the definition of
an unknown word, only to find the definition of another
word you didn’t know.
Write a short paragraph in your science journal
describing how you have discovered something by
accident.
Chapter 16
Section 3 Electricity from Magnetism
Objectives
• Explain how a magnetic field can make an electric
current.
• Explain how electromagnetic induction is used in a
generator.
• Compare step-up and step-down transformers.
Chapter 16
Section 3 Electricity from Magnetism
Electric Current from a Changing
Magnetic Field
• Faraday’s Experiment Michael Faraday conducted
an experiment trying to get the magnetic field of the
electromagnet to make an electric current in a second
wire.
Chapter 16
Section 3 Electricity from Magnetism
Electric Current from a Changing
Magnetic Field, continued
• Success for an Instant Faraday realized that
electric current in the second wire was made only
when the magnetic field was changing. The process
by which an electric current is made by changing a
magnetic field is called electromagnetic induction.
• Inducing Electric Current Look at the next slide to
see electromagnetic induction.
Chapter 16
Section 3 Electricity from Magnetism
Chapter 16
Section 3 Electricity from Magnetism
Electric Generators
• Alternating Current The electric current produced
by the generator shown on the next slide changes
direction each time the coil makes a half turn.
Because the electric current changes direction, it is an
alternating current.
• Generating Electrical Energy The energy that
generators convert into electrical energy comes from
different sources such as fossil fuels and nuclear
energy.
Chapter 16
Section 3 Electricity from Magnetism
Chapter 16
Section 3 Electricity from Magnetism
Transformers
• A transformer increases or decreases the voltage of
alternating current.
• Step Up, Step Down The number of loops in the
primary and secondary coils of a transformer
determines whether it increases or decreases the
voltage.
• Electrical Energy for Your Home The electric
current that brings electrical energy to your home is
usually transformed three times.
Chapter 16
Section 3 Electricity from Magnetism
Transformers, continued
Chapter 16
Electromagnetism
Concept Mapping
Use the terms below to complete the concept map
on the next slide.
mechanical energy
electromagnetic induction
transformers
voltage
electrical energy
electric motor
Chapter 16
Electromagnetism
Chapter 16
Electromagnetism