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Unit 11. 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. Magnets. poles – two ends of a magnet

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unit 11

Unit 11

Magnetism

magnets
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
magnets3
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
magnets4
Magnets
  • the north pole of a magnet points North
    • it is often called “North-seeking”
properties of magnets
Properties of Magnets
  • if a north pole and a south pole are brought together, they will attract each other
    • opposites attract
properties of magnets6
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
properties of magnets7
Properties of Magnets
  • like magnetic poles repel each other
  • unlike magnetic poles attract each other
magnetic fields
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 fields9
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
making a magnet
Making a Magnet
  • some magnets occur in nature
  • these magnets are called natural magnets
    • ex. magnetite (also called lodestone)
making a magnet11
Making a Magnet
  • materials that are not natural magnets can be magnetized
making a magnet12
Making a Magnet
  • magnetic induction – process by which a material can be made into a magnet
making a magnet13
Making a Magnet
  • some materials are easy to magnetize
    • ex. iron
making a magnet14
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
making a magnet15
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
the earth as a magnet
The Earth as a Magnet
  • William Gilbert
    • a British scientist
    • the Earth has north and south poles like a bar magnet
the earth as a magnet17
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 magnet18
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 magnet19
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 magnet20
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
electricity and magnetism
Electricity and Magnetism
  • Hans Oersted
    • about 200 years ago
    • an electric current flowing in a wire causes a compass needle to move
electricity and magnetism22
Electricity and Magnetism
  • an electric current passing through a wire causes a magnetic field
electricity and magnetism23
Electricity and Magnetism
  • electromagnetism – relationship between electricity and magnetism
electricity and magnetism24
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
electricity and magnetism25
Electricity and Magnetism
  • electromagnetic induction – process by which an electric current is produced by moving a wire in a magnetic field
electricity and magnetism26
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
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
electromagnets28
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
electromagnets29
Electromagnets
  • there are two ways to make an electromagnet stronger
    • increasing the number of coils
    • increasing the amount of current
electromagnets30
Electromagnets
  • electromagnets are useful because they can be turned on and off
  • electromagnets have many important uses
    • ex. radios, telephones, computers
electromagnets31
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
Transformers
  • transformer – device in which alternating current in one coil of wire induces a current in a second coil
transformers33
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
transformers34
Transformers
  • a transformer only works with alternating current
transformers35
Transformers
  • a step-up transformer increases voltage
    • it consists of more coils of wire in the secondary coil than the primary coil
transformers36
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 Motors
  • electric motor – device that changes electrical energy into mechanical energy
electric motors38
Electric Motors
  • an electric motor is made up of an electromagnet and a permanent magnet
electric motors39
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 motors40
Electric Motors
  • attraction and repulsion between the electromagnet and the permanent magnet cause the electromagnet to spin
electric motors41
Electric Motors
  • an electric motor can use direct current if a special switch is used
generators
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
generators43
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
generators44
Generators
  • most of the energy we use every day comes from generators
generators45
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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