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Magnetism UnitNotes 1
Grade 10 STJ. Kelly and A. Sanniti
Magnetic Behaviour
• After doing the lab, 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 is 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 MagneticMaterials
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 MagneticMaterials
Non- magnetic• Non-magnetic objects do not react to the
presence of a magnet. They are not attracted or repelled!
Temporary vs. Permanent Magnets
Video
• http://www.youtube.com/watch?v=uj0DFDfQajw
• http://www.youtube.com/watch?v=Dn6VVZ3mrs4&feature=related
Magnetic Properties• http://www.ndt-ed.org/EducationResources/HighSchool/Magnetism/magnetic
properties.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.cfm?id=cattle-deer-sense-magnetic-field&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…
_ +
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: