Section 1 Vocab. Magnet Magnetic poles Magnetic forces Magnetic field Magnetic field lines

Transcription

1 Magnetism Ch. 19

2 Section 1 Vocab Magnet Magnetic poles Magnetic forces Magnetic field Magnetic field lines

3 Properties of magnets In an ancient Greek city (Magnesia) 2,000 years ago people discovered a rock that could attract materials containing iron. This is where the word magnet came from

4 About 1,000 years ago people in other parts of the world discovered another property of magnetic rocks. If allowed to swing freely from a string, one part always pointed towards Polaris (North Star)_.

5 Magnets have same properties as magnetic rocks Magnets attract iron and materials that contain iron Magnets attract or repel other magnets One part of a magnet always points North when allowed to swing freely

6 Magnetic poles Any magnet, no matter is shape has two ends, each one called a pole_. The magnetic effect of a magnet is strongest at the poles The pole of the magnet that points North is the North_ pole. The pole of the magnet that points South is the _South_ pole. A magnet always has a pair of poles.

7 Magnetic Interactions What happens if you bring two like poles together? What happens if you bring two unlike poles together?

8 Magnetic force A magnetic force is produced when poles interact

9 Magnetic Fields A magnetic force is strongest at the poles, but is not limited to the poles. The area of magnetic force around a magnet is called a _magnetic field. This is why magnetics can interact without touching

10 Example of magnetic field lines The closer together the lines, the _stronger_ magnet.

11 Which magnet is stronger?

12 Single field lines Formed from one magnet

13 Combined field lines The magnetic fields of two or more magnets overlap Ex. Like poles Ex. Unlike Poles

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15 Section 2: Inside a magnet Atom Element Nucleus Proton Electron Magnetic domain Ferromagnetic material Temporary magnet Permanent magnet

16 The atom Magnetic properties of a material depend on the structure of its atoms Every atom has a center region and an outer region Center region contains protons and neutrons, called the _nucleus. Outer region is mostly empty space, but does contain _electrons_ that travel around the nucleus

17 Electron Spin Property that describes how an electron moves by spinning A spinning electron produces a magnetic field that makes the electron behave like a tiny magnet in an atom. In most atoms electrons form pairs that spin in opposite directions This produces opposite magnetic fields that cancel So most atoms only have weak magnetic properties Some atoms have unpaired electrons, these have strong magnetic properties.

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19 Magnetic Domains The magnetic fields in most materials point in random directions This results in magnetic fields canceling out So magnetic force is so small it s not noticed In certain materials the magnetic fields of many atoms are aligned with one another This is called a _magnetic domain_ The entire domain acts like a bar magnet with a North and South pole

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21 Alignment of Domains The direction in which the domains point determines if the material is magnetized or not If domains point in random directions the material is _not magnetized. Why? (what causes this) Magnetic field lines cancel out

22 If all or most of the magnetic domains are arranged in the same direction the material is _magnetized_

23 Magnetic Materials A material can be a strong magnet if its magnetic domains align These materials are called _ferromagnetic materials_ Examples: iron, nickel, cobalt, gadolinium A combination of several metals is called an _alloy_ Today the most commonly used magnets are made from _ferrite_. Mixture of substances that contain ferromagnetic elements Brittle, chips easily, but stronger and cheaper then metal magnets of the same size

24 Making and Changing Magnets Magnets can be made, destroyed, or broken Making magnets Some unmagnetized materials can be magnetized Some materials are easy to magnetize but will lose their magnetism quickly, called _temporary magnets_ Some materials are difficult to magnetize, but tend to stay magnetized longer, called _permanent magnets

25 Destroying Magnets Even strong magnets can become unmagnetized By dropping or striking hard Heating a magnet

26 Breaking Magnets What happens when a magnet is broken?

27 This happens because the domains are still aligned in each piece.

28 Section 3: Magnetic Earth Compass Magnetic declination Van Allen belts Solar wind Magnetosphere auroras

29 Earth as Magnet Sir William Gilbert Just like a bar magnet Earth has a magnetic field surrounding it and two magnetic poles.

30 Earth s Magnetic Poles Earth has geographic poles that rotate around, but also magnetic poles Located on the surface where the magnetic force is the strongest They are not in the same place as the geographic poles Magnetic North pole is in _Northern Canada_.

31 Magnetic Declination You must account for the fact that the geographic poles are different from the magnetic poles The angle between the geographic poles and the magnetic poles is called _magnetic declination_ This differs based on your position on Earth

32 The magnetic Poles do not stay in the same place

33 Earth s Magnetic Field Earth leaves a Record

34 The Magnetosphere Earth s magnetic field extends into space Earth s magnetic field affects the movement of electrically charged particles in space. One region is called _Van Allen belts_. These doughnut shaped regions containing electrons and protons that move at very high speeds

35 Solar Wind Other electrically charged particles in space come from the sun _Solar wind_ is a stream of electrically charged particles from the sun. It pushes against the Earth s magnetic field and surrounds the field This region shaped by solar winds is called the _magnetosphere_

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37 Auroras When high speed, charged particles get close to Earth s surface they interact with atoms of the atomsphere This causes some of the atoms to give off light This is seen in the Northern hemisphere and is called _Northern lights or Aurora Borealis_ It is called the Southern lights or Aurora Australis in the Southern hemisphere.

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