Download Magnetism

Magnetism Unit
Notes 1
Grade 10 ST
Magnetic Behaviour
• After watching the demo, what conclusions
can you make about what you saw?
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What is Magnetism?
• Magnetism is the force of attraction or
repulsion in and around a material
• Magnetism is present in all materials but at
such low levels that it is not easily detected
• Certain materials such as magnetite, iron,
steel, nickel, cobalt exhibit magnetism at
levels that are easily detectable
What is a Magnet?
• A magnet is any piece of material that has the
property of attracting iron (or steel).
• Magnetite, also known as lodestone, is a
naturally occurring rock that is a magnet.
• This natural magnet was first discovered in a
region known as Magnesia in Greece and was
named after the area in which it was
discovered.
What is a Magnet? Cont’d
• Magnetism may be naturally present in a material
or the material may be artificially magnetized by
various methods.
• Magnets may be permanent or temporary.
– After being magnetized, a permanent magnet will
retain the properties of magnetism indefinitely.
– A temporary magnet is a magnet made of soft iron,
that is usually easy to magnetize; however, temporary
magnets lose most of their magnetic properties when
the magnetizing cause is discontinued.
Different Types of Magnetic
Materials
Magnetic
• A permanent magnet
• Two magnetized objects can attract or repel
each other
Different Types of Magnetic
Materials
Ferromagnetic
• Materials which can be magnetized are called
ferromagnetic materials
• They contain iron, nickel or cobalt
• They are attracted to magnetic objects, they become
temporarily magnetized
• Example: Iron
– Iron is made up of a set of regions called domains.
– Each domain acts like a tiny magnet with it’s own north
and south poles
– When iron is not magnetized= domains are not aligned
– When iron is magnetized domains are aligned
Different Types of Magnetic
Materials
Non- magnetic
• Non-magnetic objects do not react to the
presence of a magnet. They are not attracted
or repelled!
Temporary vs. Permanent Magnets
Magnetic Properties
•
http://www.ndted.org/EducationResources/HighSchool/Magnetism/magneticproperties.htm
• After watching the above applet, explain what
happens when a magnet is broken into smaller
pieces
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Magnetic Properties
• Magnets can be cut into smaller and smaller
pieces indefinitely
• All magnets have a north seeking and south
seeking pole
• Each new piece makes a new magnet with it’s
own north and south poles.
• The NORTH POLE of a magnet is the end that
naturally seeks the earth’s magnetic pole near
the geographic north pole
Magnetic Properties
• Magnets interact with each other through forces
of attraction and repulsion
• In general, the following is true of magnetic poles
– Opposite magnetic poles attract
– Like magnetic poles repel each other
Question: Knowing this, is the North Pole a North Pole
or a South Pole? _____________________________
Magnetic Properties Check
• If the north pole of a magnet is moved toward
the south pole of another magnet, will the
north pole be subjected to an attractive or a
repulsive force? Explain your answer.
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Interesting Article
• http://www.scientificamerican.com/article.cf
m?id=cattle-deer-sense-magneticfield&print=true
Magnetic Fields
• In a magnetized object, the domains are all
lined up in the same direction.
• Any magnetized object produces a magnetic
field. The magnetic field is the area around
the magnet where the magnetic force can be
felt.
Magnetic Fields
• To draw the magnetic field, we use arrows.
• Most magnets have 2 poles: north (N) and
south (S)
• Two possible forces exist between
magnetized objects
• Attraction
• Repulsion
Magnetic Field
around a bar
magnet
•Arrows are always
pointing towards
the south
Compasses
How do compasses work?
• The north needle of a
compass always points
in the same direction as
the magnetic field.
Magnetic field around a straight wire
• When there is a current flowing through a
wire, there is a magnetic field around the
wire.
• The shape of the magnetic field is individual
circles around the wire.
Magnetic Field around a Straight Wire
To determine the direction of the magnetic field
lines we use the “Right Hand Rule”
• Place your right thumb along the direction of
the current.
• Your fingers curl in the same direction as the
magnetic field
Magnetic Field around a Straight
Wire
Try it…
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Magnetic Field around a Straight
Wire
• In a circuit
• With Compass
Magnetic Field around
Electromagnets
• When there is a current flowing through a
coiled wire, there is a magnetic field that is
created we call it an electromagnet.
• The shape of the magnetic field around the
electromagnet is exactly the same as around a
bar magnet
Magnetic Fields around
Electromagnets
• To determine the location of N and S, we use
the “Second Right Hand Rule”
• Place your fingers on your right hand so that they curl
in the same direction as the current.
• Your thumb indicates north
Magnetic Fields around
Electromagnets
• Try it…
• With Compass
Factors that affect the strength of
an electromagnet
• To increase the strength of an electromagnet:
– Increase current
– More coils
– Type and gauge of the conductor
– The core material
Induction in an
Electromagnet
• To generate a magnetic field:
Induction in an
Electromagnet
• To generate an electric current: