Transcript Magnets and Electromagnets

Magnetism
Magnets

magnetism – force of attraction or
repulsion

not all objects are affected by the force of
magnetism


ex. wood, glass, paper, plastic
common metals affected by magnetism are
iron, nickel, and cobalt
Atoms themselves have magnetic properties due
to the spin of the atom’s electrons.
Groups of atoms join so that their magnetic fields
are all going in the same direction
These areas of atoms are called “domains”
When an unmagnetized substance is placed in a magnetic
field, the substance can become magnetized.
This happens when the spinning electrons line up in the
same direction.
Magnets

poles – two ends of a magnet

every magnet has two poles
north (N) pole
 south (S) pole


even if you break a magnet in half, each half
will have a north pole and a south pole
Properties of Magnets

like magnetic poles repel each other

unlike magnetic poles attract each other
Magnetic Fields

magnetic field – area around a magnet
where magnetic forces can act

a magnetic field is made up of magnetic
lines of force
Magnetic Fields

magnetic lines of force – lines that show
the shape of a magnetic field

the magnetic lines of force are closest
together at the poles of the magnet

this is where the magnet is strongest
Field Lines Around a Bar Magnet
Field Lines of Repelling Bars
Field Lines of Attracting Bars
S
N
S
you get 2 magnets!
N
S
N
The Earth as a Magnet

the Earth has a North Magnetic Pole and
a South Magnetic Pole

the North Magnetic Pole is located near the
geographic North Pole

the South Magnetic Pole is located near the
geographic South Pole
The Earth as a Magnet

the North Magnetic Pole is like the south
pole of a bar magnet

the South Magnetic Pole is like the north
pole of a bar magnet
The Earth as a Magnet

the Earth is surrounded by a magnetic
field which extends far into space

magnetosphere – region of the Earth’s
magnetic field
The Earth as a Magnet
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the magnetosphere traps charged
particles from the sun

when these particles enter the
atmosphere, an aurora is formed

auroras are also called the northern and
southern lights
Electricity and Magnetism

an electric current passing through a
wire causes a magnetic field
Electricity and Magnetism

electromagnetism – relationship between
electricity and magnetism
Electricity and Magnetism

electromagnetic induction – process by
which an electric current is produced by
moving a wire in a magnetic field
Electricity and Magnetism

a wire carrying an electric current always
has a magnetic field around it
the magnetic field in a straight wire is not
very strong
 if the wire is wound into a coil, the magnetic
field becomes much stronger as the
individual magnetic fields overlap


the greater the number of coils, the stronger the
magnetic field
Electromagnets

electromagnet – temporary magnet
made by wrapping a current-carrying
wire around an iron core

the center of an electromagnet is called the
core

it is often made of iron
Electromagnets

as long as current is flowing, an
electromagnet has a magnetic field

when current is turned off, there is no
longer a magnetic field
Electromagnets

there are two ways to make an
electromagnet stronger

increasing the number of coils

increasing the amount of current
A Simple Electromagnet:
Electromagnets

electromagnets are useful because they
can be turned on and off

electromagnets have many important
uses

ex. radios, telephones, computers
Electromagnets

changing the direction of an electric
current causes the poles of an
electromagnet to reverse

this feature is important in the production of
electric motors
Transformers

transformer – device in which alternating
current in one coil of wire induces a
current in a second coil
Transformers

a transformer consists of two coils of
wire around a magnet
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the first coil, called the primary coil, is
connected to the power source
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the second coil, called the secondary coil, is
connected to the load

a load is something that uses electricity, such as
a light bulb or a motor
Transformers

a transformer only works with alternating
current
Transformers

a step-up transformer increases voltage

it consists of more coils of wire in the
secondary coil than the primary coil
Transformers

a step-down transformer decreases
voltage

it consists of more coils of wire in the
primary coil than the secondary coil
Electric Motors

electric motor – device that changes
electrical energy into mechanical energy
Electric Motors

an electric motor is made up of an
electromagnet and a permanent magnet
Electric Motors

the electromagnet is free to turn and is
hooked up to a source of alternating
current

changing the direction of an electric current
causes the poles of an electromagnet to
reverse
Electric Motors

attraction and repulsion between the
electromagnet and the permanent
magnet cause the electromagnet to spin
Generators

generator – device that changes
mechanical energy into electrical energy

a current can be induced in a loop of wire by
spinning the loop inside a magnetic field

due to the changing direction of the wire, an
alternating current is produced
Generators

an electric generator is made up of an
insulated loop of wire and a U-shaped
magnet

spinning the loop of wire in the magnetic
field of the magnet produces an electric
current
Generators

most of the energy we use every day
comes from generators
Generators
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mechanical energy for many generators
is supplied by turbines

a turbine is a large wheel that is turned by
moving steam or water