18.1 Magnets and Magnetic Fields - Magnets and Magnetic Fields What is an example of how you use magnets? 11/12/2016 2 Magnets around the House: ... attraction or repulsion between

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  • 11/12/2016


    Physical Science


    Bill Nye-Magnetism Video

    What happens when the poles of two magnets are thought close together?

    What causes a magnet to attract or repel another magnet?

    How is Earths magnetic field oriented?

    18.1 Magnets and Magnetic Fields

    What is an example of how you use magnets?


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    Magnets around the House:Headphones

    Computer speakers

    Telephone receiversPhone ringers

    Microwave tubesSeal around refrigerator door

    Credit card magnetic strip

    TV deflection coilComputer monitor

    Computer hard drive

    Shower curtain weights / attach to tubPower supply transformers

    Magnets inside of motors:

    CD and DVD spinner and head positioner

    Audio and VHS tape transport

    VHS tape loader Microwave stirring fans

    Kitchen exhaust fans Garbage disposal motor

    Sump pump Furnace blower and exhaust

    Garage door opener Bathroom exhaust fan

    Electric toothbrush Ceiling fan

    Pager or cell phone vibrator

    Clocks (not the wind-up type or LCD type)


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    Magnets in your Car:Starter motor

    A/C clutch

    Interior fan motor

    Electric door locks

    Windshield wiper motor

    Electric window motor

    Side-view mirror adjuster motor

    CD/tape player motor and playback

    Engine speed sensors


    Starter relay

    Windshield washer pump motor

    More than 3,000 years ago Greeks discovered deposits of a mineral that was a natural magnet.

    The mineral is now called magnetite.

    Ex: lodestone


    These magnets were used by the ancient peoples as compasses to guide sailing vessels.

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    Today, the word magnetism refers to the properties and interactions of magnets.


    magnet any material that attracts iron and materials that contain iron

    magnetism the attraction or repulsion of magnetic materials

    Magnets attract or repel other magnets.

    Common metals affected by magnetism are iron, nickel, and cobalt


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    Nonmagnetic materials, such as plastic, glass and wood, have electrons that flow in different directions.

    Magnetic poles are where the magnetic force exerted by the magnet is strongest. the two ends on any magnet, no matter what its shape

    All magnets have a north pole and a south pole.

    Magnetic Poles

    magnetic force the attraction or repulsion between magnetic poles



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    Magnetic poles

    that are alike

    repel each other.

    Magnetic poles that

    are unlike attract

    each other.

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    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


    Magnetic Poles

    Poles- two ends of a magnet

    No Monopoles Allowed

    It is not possible to end up with a single North pole or a single South pole, which is a monopole ("mono" means one or single, thus one


    S N

    Recall that even individual atoms of magnetic materials act as tiny magnets.

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    Making a Magnet

    materials that are hard to magnetize

    will also stay magnetized for a long


    a magnet that is hard to magnetize

    but tends to keep its magnetism is

    called a permanent magnetEx: Cobalt, Nickel, Aluminum

    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 magnetEx: Iron nails


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    The two ends of a horseshoe-shaped magnet are the north and south poles.

    A magnet shaped like a disk has opposite poles on the top and bottom of the disk.

    Where are the Poles on different shaped magnets?

    Magnetic field lines always connect the north pole and the south pole of a magnet.

    Magnetic Fields

    A magnet has a

    magnetic field

    distributed throughout

    the surrounding space

    Michael Faraday realized that ...

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    A magnet is surrounded by a magnetic field.

    A magnetic field exerts a force on other magnets and objects made of magnetic materials.

    The magnetic field is strongest close to the magnet and weaker far away.

    A magnetic field also has a direction & illustrated by arrows.

    magnetic field lines the lines that map

    out the magnetic field around a magnet

    Magnetic field lines spread out from one pole, curve around the magnet, and return to the other pole

    forming a closed loop.

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    The density of field

    lines indicates the

    strength of the field

    Magnetic Field


    Field Lines Around Magnets

    Bar Sphere

    Repelling Attracting


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    magnetic domain a

    grouping of billions of atoms that have their

    magnetic fields lined up in the same


    Atoms electronsspin around when placed near a magnetic field.

    An unmagnetized substance looks like this

    While a magnetized substance looks like this

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    Earth as a Magnet

    Earth has a magnetic field with two main poles.

    This magnetic field enables us to use compasses

    Our planet's rotation causes molten iron-nickel in its outer core to circulate creating electrical

    currents and a magnetic field.

    Earth as a Magnet

    William Gilbert

    a British scientist

    Showed that the Earth behaves as a magnet

    Earth has north and south poles like a

    bar magnet

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    The Earths Magnetic Field

    The Earth is surrounded by a magnetic field which extends far into

    space. Called the magnetosphere

    Magnetic poles of the Earth are

    different from the geographic poles of

    the Earth

    Earth as a Magnet

    the North Magnetic

    Pole is located near

    the geographic

    South Pole

    the South Magnetic

    Pole is located near

    the geographic North


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    Earths magnetic poles move slowly with time.

    Earths Magnetic Poles

    Sometimes Earths magnetic poles switch places so that Earths south magnetic pole is the southern hemisphere near the geographic south pole.



    Compasses are used to determine direction

    Compass needles are magnetized and respond to the magnetic field of the Earth

    We use the Earths magnetic field to find direction. Migration of birds

    The needle of a compass always points toward the magnetic south pole.

    The compass needle points toward the geographic North


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    Magnetic Effects

    The most visible effect of the earths magnetic field is a colorful light display, called an aurora

    Collisions between the charged particles and other particles in the upper atmosphere create glowing lights


    18.2 Magnetism from Electric


    What happens to a compass near

    a wire that is carrying a current?

    Why are electric motors useful?


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    In 1820, Han Christian Oersted, a Danish physics teacher, found that electricity and magnetism are related.

    Oersted hypothesized:

    Electric current must produce a magnetic field around the wire, and the direction of the field changes with the direction of the current.

    When a compass was brought

    near electric current, the

    compass needle no longer

    pointed north

    When an electric current passes through a wire a magnetic field is formed.

    The magnetic field depends on the direction of the current in the wire.


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    The direction of the magnetic field around the wire reverses when the direction of the current in the wire reverses.

    As the current in the wire increases the strength of the magnetic field increases.


    Electromagnetism relationship between electricity

    and magnetism

    Oersteds discovery is responsible for the invention of

    new tools based on the principles of electromagnetism.


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    When an electric current is passed through a coil of wire wrapped around a metal core, a very strong magnetic field is produced. This is called an electromagnet.

    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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    Electromagnets can be turned on and off

    You can make an electromagnet