Transcript magnetic field

Chapter 16 Section 1
Objective:
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.
• Properties:
• Magnetic Poles are points on a
magnet that have opposite
magnetic qualities.
• 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.
• 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.
• A magnetic field exists in the
region around a magnet in which
magnetic forces can act.
• Why are some materials
magnetic and some not?
• 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.
• 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.
• When you cut a magnet in half, you end up with
two magnets.
• 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 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.
• Name two examples of the
effect of Earth’s magnetic
field.
• The Earth behaves as if it has a bar
magnet running through its center.
• The point of a compass needle is
attracted to the south pole of a
magnet. Opposite poles of magnets
attract each other.
• A compass needle points north
because the magnetic pole of Earth
that is closest to the geographic North
Pole is a magnetic south pole.
• Scientists think that the Earth’s
magnetic field is made by the
movement of electric charges in
the Earth’s core.
• 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 2 Objective:
• Identify the relationship between
an electric current and a magnetic
field.
• Compare solenoids and
electromagnets.
• electromagnetism—the interaction
between electricity and magnetism.
• 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. 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 3
Objective:
• 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.
• Michael Faraday conducted an experiment
trying to get the magnetic field of the
electromagnet to make an electric current in
a second wire.
• 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.
• The electric current produced by
the generator changes direction
each time the coil makes a half
turn. Because the electric current
changes direction, it is an
alternating current. The energy that
generators convert into electrical
energy comes from different
sources such as fossil fuels and
nuclear energy.
• A transformer increases or
decreases the voltage of alternating
current.
• The number of loops in the
primary and secondary coils of a
transformer determines whether it
increases or decreases the voltage.
• The electric current that brings
electrical energy to your home is
usually transformed three times.