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Magnetism

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Unit 11 Magnetism – PowerPoint PPT presentation

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Title: Magnetism


1
Unit 11
  • Magnetism

2
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

3
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

4
Magnets
  • the north pole of a magnet points North
  • it is often called North-seeking

5
Properties of Magnets
  • if a north pole and a south pole are brought
    together, they will attract each other
  • opposites attract

6
Properties of Magnets
  • if the north pole of one magnet is brought near
    the north pole of another magnet, they will repel
    each other
  • if two south poles are brought together, they
    will repel each other

7
Properties of Magnets
  • like magnetic poles repel each other
  • unlike magnetic poles attract each other

8
Magnetic Fields
  • magnetic field area around a magnet where
    magnetic forces can act
  • a magnetic field is made up of magnetic lines of
    force

9
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

10
Making a Magnet
  • some magnets occur in nature
  • these magnets are called natural magnets
  • ex. magnetite (also called lodestone)

11
Making a Magnet
  • materials that are not natural magnets can be
    magnetized

12
Making a Magnet
  • magnetic induction process by which a material
    can be made into a magnet

13
Making a Magnet
  • some materials are easy to magnetize
  • ex. iron

14
Making a Magnet
  • a material that is easily magnetized tends to
    lose its magnetism quickly
  • a magnet made of this kind of material is called
    a temporary magnet

15
Making a Magnet
  • materials that are hard to magnetize will also
    stay magnetized for a long time
  • a magnet that is hard to magnetize but tends to
    keep its magnetism is called a permanent magnet

16
The Earth as a Magnet
  • William Gilbert
  • a British scientist
  • the Earth has north and south poles like a bar
    magnet

17
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

18
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

19
The Earth as a Magnet
  • the Earth is surrounded by a magnetic field which
    extends far into space
  • magnetosphere region of the Earths magnetic
    field

20
The Earth as a Magnet
  • 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

21
Electricity and Magnetism
  • Hans Oersted
  • about 200 years ago
  • an electric current flowing in a wire causes a
    compass needle to move

22
Electricity and Magnetism
  • an electric current passing through a wire causes
    a magnetic field

23
Electricity and Magnetism
  • electromagnetism relationship between
    electricity and magnetism

24
Electricity and Magnetism
  • Michael Faraday (British scientist)
  • Joseph Henry (American scientist)
  • when a wire is moved across a magnetic field, an
    electric current is induced in the wire

25
Electricity and Magnetism
  • electromagnetic induction process by which an
    electric current is produced by moving a wire in
    a magnetic field

26
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

27
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

28
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

29
Electromagnets
  • there are two ways to make an electromagnet
    stronger
  • increasing the number of coils
  • increasing the amount of current

30
Electromagnets
  • electromagnets are useful because they can be
    turned on and off
  • electromagnets have many important uses
  • ex. radios, telephones, computers

31
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

32
Transformers
  • transformer device in which alternating current
    in one coil of wire induces a current in a second
    coil

33
Transformers
  • a transformer consists of two coils of wire
    around a magnet
  • the first coil, called the primary coil, is
    connected to the power source
  • 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

34
Transformers
  • a transformer only works with alternating current

35
Transformers
  • a step-up transformer increases voltage
  • it consists of more coils of wire in the
    secondary coil than the primary coil

36
Transformers
  • a step-down transformer decreases voltage
  • it consists of more coils of wire in the primary
    coil than the secondary coil

37
Electric Motors
  • electric motor device that changes electrical
    energy into mechanical energy

38
Electric Motors
  • an electric motor is made up of an electromagnet
    and a permanent magnet

39
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

40
Electric Motors
  • attraction and repulsion between the
    electromagnet and the permanent magnet cause the
    electromagnet to spin

41
Electric Motors
  • an electric motor can use direct current if a
    special switch is used

42
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

43
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

44
Generators
  • most of the energy we use every day comes from
    generators

45
Generators
  • mechanical energy for many generators is supplied
    by turbines
  • a turbine is a large wheel that is turned by
    moving steam or water
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