Magnetism

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Magnetism
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Magnets

• A special stone first discovered lt2000 years ago
  in Greece, in a region called Magnesia,
  attracted iron, they called it magnetite hence
  the magnet name.
• 2. About 1000 years ago they noticed that a
  hanging magnet always pointed to the North Star
  A.K.A Lodestar. Hence the other name for
  naturally occurring magnets lodestone

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Properties of Magnets

• You can investigate the properties of magnets by
  bringing two magnets together.
• The ends of the magnets attract each other and
  stick together.
• The ends of the magnets repel each other and the
  magnets move apart.

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Magnetic Poles

• Magnetic Poles the ends of the magnet, area
  where the magnetic effect is the strongest.
• If a bar magnet is suspended by a thread or
  string, it will align itself so that one strong
  end points north and the other points south,
  hence the names for the North and South poles
  of the magnet.
• Like poles of separate magnets repel push away
  from each other
• Unlike poles attract each other

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Magnetic Field

• The area of magnetic force surrounding a magnet.
• The magnetic fields is strongest at the poles of
  a magnet, but exists around the entire magnet.
• Magnetic field lines exists from one pole to the
  other.

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• The number of field lines in any given region
  indicates the relative strength of the field
• Although the magnetic field is invisible you can
  see its effect around a magnet by placing a piece
  of paper on top of a magnet and then sprinkling
  iron fillings over the paper
• If you were to place a magnetic material, such as
  iron, near the magnet it would be most attracted
  to either the north or south pole

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• Iron would also be attracted by the magnetic
  field around the magnet
• What do you think happens if you place the entire
  magnet in a dish of iron filings

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Magnetic fields
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Attract Repel

• Magnets attract because force comes out of North
  Pole and goes into the South Pole

Attraction
Repulsion

• Magnets repel because the forces are pushing away
  from each other

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Magnets

• If you snap a magnet in half, the inside pieces
  become the opposite poles

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Inside a Magnet

• At the atomic level, there are protons ( charge)
  neutrons (neutral charge) in the nucleus, and
  electrons (- charge) spinning in orbits around
  the nucleus. The moving electron acts as a mini
  electrical charge and therefore has a magnetic
  field associated w/ it.
• In ferrous materials clusters of atoms align
  their atoms w/ one another. A cluster of billions
  of atoms w/ magnetic fields aligned is called a
  domain.

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Inside a Magnet

• When domains are randomly arranged forces
  cancel each other out. no net magnetic affect
• When domains have their magnetic affect in
  alignment - forces are additive and create a
  strong magnetic affect

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Magnetic Fields

• that region around a magnet that is affected by
  the magnet. Strongest at the poles, the Force
  forms lines that go out of the North Pole and
  wrap back around to enter in at the South Pole.

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Magnetic Field

• Magnetic field lines exists from one pole to the
  other.
• The number of field lines in any given region
  indicates the relative strength of the field

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Magnetic Materials

• The electrons of all atoms spin as they move
  about the nucleus
• A spinning electron produces a magnetic field
  with both a north and south pole
• In most materials, the magnetic fields of
  individual atoms cancel each other, so the
  materials arent magnetic
• In certain materials this isnt the case

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• The poles line up in the same direction in
  microscopic magnetic regions, called magnetic
  domains
• When all the domains are arranged with their
  poles in the same direction, the iron bar becomes
  a permanent magnet
• When the domains are arranged randomly, the iron
  bar is not magnetized

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Making Magnets

• Since Magnetism and electricity are so closely
  related, it is relatively easy to make magnets
• Temporary magnets materials that become
  magnetized while in contact w/ strong magnets
  ie a paperclip is able to pick up more paper
  clips when stuck to a strong magnet
• Permanent magnets materials that maintain their
  magnetism when the magnet is removed from it.

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Earth As A Magnet

• If you hang a magnet by a string, the north
  seeking pole will always point north because the
  earth itself is a huge magnet
• An instrument that takes advantage of the earths
  magnetic field is the compass
• A compass has a magnetized needle in it that
  turns freely
• The north and south pole of the earths axis are
  referred to as geographic north pole sometimes
  called true north

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Magnetic Earth

• Earths core is Iron Earth is a giant magnet
• Earths magnetic north pole is not the same as
  Earths axis north pole. It is about 1250 km (776
  miles) away from the true north pole
• The angle between true north and magnetic north
  is the magnetic declination.

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• Evidence suggests that the earths magnetic field
  is caused by the movement of molten metals near
  the earths core
• Measurements show that the earths magnetic poles
  change position over time
• Changes in the flow of the molten metals inside
  the earth may cause the magnetic poles to move

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Magnetic Effects

• The most visible effect of the earths magnetic
  field is a colorful light display, called an
  aurora
• An aurora hangs like a curtain of light
  stretching over the polar regions of the earth
• Collisions between the charged particles and
  other particles in the upper atmosphere create
  glowing lights

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Aurora
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Aurora
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Aurora
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• The color of aurora depends on the kind of atoms
  in the atmosphere
• Magnetic storms interfere with compass needles
  and radio and television waves.
• Magnetic storms occur when solar flares produce
  charged particles that become trapped in the
  earths magnetic field.

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• Earths magnetic field affects living things.
• They have magnetic particles inside their bodies
• These particles help organisms using the magnetic
  field to find their way.

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Electromagnetism

• In 1820, Christian Oersted, a Danish physicist
  made an observation that when a compass was
  brought near electric current, the compass needle
  no longer pointed north. It turned 90 degrees.
• The compass needle turned in the opposite
  direction when he reversed the current.

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• He hypothesized that when an electric current
  flowed through it, the wire acted like a magnet.
  Somehow electricity could produce magnetism.

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• The greater number of turns a coil has, the
  stronger the magnetic field can produce.
• The greater the size of the soft-iron core, the
  stronger the magnet is.
• When a magnet is turned on an electric current
  flows through the wire coil, creating a magnetic
  field around the coil.
• The magnetic domains in the soft-iron core align
  with the magnetic field of the coil.

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• The soft-iron core becomes magnetized.
• One end of the soft-iron core is a north pole,
  and the other end is the south pole.
• The magnetic field of the magnetized soft-iron
  core combines with the magnetic field of the wire
  coil. The combined magnetic fields create a very
  strong magnet.

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• Pure iron is referred to as soft iron.
• An electromagnet exerts a magnetic force that can
  make things move.

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Electromagnets

• Oersteds discovery is responsible for the
  invention of new tools based on the principles of
  electromagnetism.
• Electromagnet a magnet made of a soft-iron core
  surrounded by a coil of wire through which an
  electric current passed.
• The strength depends on the number of turns in
  the coil, the amount of current, and the size of
  the iron core.

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Electric Motors

• An electromagnet, called an armature, is placed
  in the magnetic field of permanent magnet.
• When current flows through the electromagnet, its
  poles repel the like poles of the permanent
  magnets.
• When the direction of the current changes, the
  poles on the electromagnet reverse, and the
  electromagnet spins

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• The commutator is split metal ring that acts as
  as a switch
• The commutator reverses the current in the
  electromagnet
• Electric current enters the electromagnet through
  brushes that touch the spinning communtator rings

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Current Meters

• The response of magnetic forces between an
  electromagnet and a permanent magnet is used in
  various kinds of meters

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Current Meters

• The two springs connected to the rod through the
  electromagnet control the pointer of the
  galvanometer
• When an electric current passes the
  electromagnet, the poles of the electromagnet
  respond to the poles of the permanent magnet

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Electric Current Magnetic Fields

• When electric charges run thru a wire they create
  an electric current a flow of charge thru a
  material
• An electric current produces a magnetic field
• An electric current through a coil of wire around
  a nail produces a magnet
• Electric circuit a complete path through which
  electric current can flow
• Each circuit has a source of electrical energy
• Have devices that are run by the electric current
• Connected by conducting wires and a switch

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Electromagnetic induction

• The process of inducing a current by moving a
  magnetic field through a wire coil without
  touching it.
• This occurs any time motion takes place between
  the wire and the magnetic field.
• A weak current is produced when the movement of
  the wire is slow.
• A strong current is produced when the movement is
  fast.

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Generators

• Devices for converting mechanical energy to
  electrical energy.
• Spin a coil of wire through a magnetic field
• Will make a current flow through wire
• Make alternating current as the go past the
  different poles of the magnet.

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Transformer

• Changes the voltage of alternating current
• Power comes at high voltage because the power
  company loses less energy.
• A step-down transformer lowers the voltage to
  120V or 240V for your house
• Uses two coils of wire and a soft iron core
• Primary coil in
• Secondary coil out

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Step-down Transformer

• Has more coils on primary than secondary
• Decreases voltage

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Step-Up Transformer

• Has more coils on secondary than primary
• Increases voltage