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Electricity, Sound and Light
Chapter Eight: Electricity and
Magnetism
• 8.1 Electricity
• 8.2 Electrical Circuits and Electrical
Power
• 8.3 Properties of Magnets
Investigation 8B
Magnetism
• What are the properties of magnets?
8.3 Properties of Magnets
• If a material is magnetic, it has the ability to
exert forces on magnets or other magnetic
materials.
• A magnet is a material that can create
magnetic effects by itself.
Which of these is a permanent magnet?
8.3 The magnetic field
• A magnet fills the space
around itself with a kind of
potential energy called
the magnetic field.
• You can see the pattern
of the magnetic field by
sprinkling iron filings on
cardboard then placing a
magnet underneath.
8.3 The magnetic field
• The force from a
magnet gets weaker
as it gets farther
away.
• Separating a pair of
magnets by twice
the distance
reduces the force by
8 times or more.
8.3 How does a compass work?
• A compass needle is a
magnet that is free to
spin.
• The north pole of a
compass needle
always points toward
the south pole of a
permanent magnet.
8.3 How does a compass work?
• The planet Earth has a
magnetic field that
comes from the core
of the planet itself.
8.3 How does a compass work?
• When you use a compass, the north-pointing end of
the needle points toward a spot near (but not
exactly at) Earth’s geographic north pole.
• The south magnetic pole of the planet is near the
geographic North Pole.
8.3 The effect of current on a
magnet
• In 1819, Hans Christian Øersted placed a compass
needle near a wire in a circuit.
• When a switch in the circuit was closed, the
compass needle moved just as if the wire were a
magnet.
8.3 Magnetic forces and electric
current
• A magnet made with
wires and electric current
is called an
electromagnet.
• The electromagnet
produces a magnetic field
exactly the same as a
permanent magnet with
its north and south poles.
8.3 The right hand rule
• When the fingers of your
right hand curl in the
direction of current, your
thumb points toward the
electromagnet’s north
pole.
• You can switch the north
and south poles of an
electromagnet by
reversing the direction of
the current in the coil.
8.3 Magnetic forces and electric
current
• The metals iron, nickel, and
cobalt have strong magnetic
properties.
• Both permanent magnets
and iron owe their magnetic
properties to their atoms.
• Iron atoms can easily rotate
their magnetic poles to line
up with neighboring atoms.
8.3 Electric generators and induction
• The process of using a
moving magnet to create
electric current or voltage
is called electromagnetic
induction.
• A moving magnet induces
electric current to flow in a
circuit.
• The word “induce” means
“to cause to happen.”
8.3 Transformers
• A transformer
changes the high
voltage from the
main power lines
to the 120 volts
your appliances
use.
8.3 Transformers
• Inside a transformer, the
input is connected to the
primary coil.
• The output of the
transformer is connected
to the secondary coil.
• The two coils have
different numbers of
turns to convert from one
voltage to another.
8.3 Alternating current
• Your house uses alternating current or AC at
either 120 or 220 volts.
• AC voltage reverses direction 60 times per
second.
Technology Connection
Household Electricity
• You use electric current
every day.
• When you plug in an
electric appliance, you
connect it to a circuit
created by wires in the
walls.
Activity
Make a Simple Motor
• Electricity and
magnetism are two
forms of the same
basic force.
• You will use this
idea to create a
small motor.