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Unit 11 PowerPoint PPT Presentation


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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

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Unit 11 l.jpg

Unit 11

Magnetism


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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


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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


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Magnets

  • the north pole of a magnet points North

    • it is often called “North-seeking”


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Properties of Magnets

  • if a north pole and a south pole are brought together, they will attract each other

    • opposites attract


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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


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Properties of Magnets

  • like magnetic poles repel each other

  • unlike magnetic poles attract each other


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Magnetic Fields

  • magnetic field – area around a magnet where magnetic forces can act

    • a magnetic field is made up of magnetic lines of force


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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


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Making a Magnet

  • some magnets occur in nature

  • these magnets are called natural magnets

    • ex. magnetite (also called lodestone)


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Making a Magnet

  • materials that are not natural magnets can be magnetized


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Making a Magnet

  • magnetic induction – process by which a material can be made into a magnet


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Making a Magnet

  • some materials are easy to magnetize

    • ex. iron


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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


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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


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The Earth as a Magnet

  • William Gilbert

    • a British scientist

    • the Earth has north and south poles like a bar magnet


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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


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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


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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


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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


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Electricity and Magnetism

  • Hans Oersted

    • about 200 years ago

    • an electric current flowing in a wire causes a compass needle to move


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Electricity and Magnetism

  • an electric current passing through a wire causes a magnetic field


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Electricity and Magnetism

  • electromagnetism – relationship between electricity and magnetism


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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


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Electricity and Magnetism

  • electromagnetic induction – process by which an electric current is produced by moving a wire in a magnetic field


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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


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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


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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


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Electromagnets

  • there are two ways to make an electromagnet stronger

    • increasing the number of coils

    • increasing the amount of current


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Electromagnets

  • electromagnets are useful because they can be turned on and off

  • electromagnets have many important uses

    • ex. radios, telephones, computers


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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


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Transformers

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


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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


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Transformers

  • a transformer only works with alternating current


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Transformers

  • a step-up transformer increases voltage

    • it consists of more coils of wire in the secondary coil than the primary coil


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Transformers

  • a step-down transformer decreases voltage

    • it consists of more coils of wire in the primary coil than the secondary coil


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Electric Motors

  • electric motor – device that changes electrical energy into mechanical energy


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Electric Motors

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


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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


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Electric Motors

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


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Electric Motors

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


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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


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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


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Generators

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


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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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