History of the Magnet:

Transcription

1 Magnets

2 History of the Magnet: More than 2,000 years ago, people living in Magnesia, Greece, discovered an unusual rock. The rock attracted materials that contained iron.

3 The rock they found contained a mineral called magnetite. Both the word magnetite and magnet come from the word Magnesia. Magnetism-the th attraction of a magnet for another object.

4 About 1,000 years ago, people in other parts of the world discovered another interesting property of magnets if they allowed the magnetic rock to swing freely from a string, one part of the rock would always point in the same direction.

5 That direction was toward a certain northern star, called the leading star, or lodestar. Magnetic rocks = lodestones.

6 Lodestone/Magnetic Rocks

7 Magnetic Poles Any magnet, NO MATTER WHAT ITS SHAPE, has two ends, each one called a magnetic pole. The pole of the magnet is where the magnetic effect is the greatest!

8 Magnetic Poles One pole of the magnet will always point north and is labeled the north pole. The other end is labeled the south pole.

9 Interactions Between Magnetic Poles What happens when you bring two magnets together? The answer depends on how you hold the poles of the magnets.

10 North to North South to South Magnetic Poles that are alike repel each Magnetic Poles that are alike repel each other.

11 North to South Magnetic poles that are unlike attract each other. Opposites Attract

12 The force of attraction or repulsion between magnetic poles is magnetism. Any material that exerts magnetic forces is considered a magnet.

13 Interactions Between Magnetic Poles Japan has a high-speed train that is moved by strong magnets instead of wheels. It is called a magnetically levitating train, or maglev train. Magnets in the bottom of the train and in the guide- way on the ground have like poles. Since like poles repel, the two magnets push each other away. The result is that the train car is lifted up, or levitated. Other magnets push and pull the train forward.

14 Maglev Train

15 Paired Poles What do you think happens if you break a magnet in two? You now have two separate magnets! Do you have a north pole in one hand and a south pole in the other hand? NO!

16 Magnetic Fields The magnetic force is stronger at the poles of a magnet, but it is not limited to the poles. Magnetic forces are exerted all around a magnet. The region of magnetic force around a magnet is known as its magnetic field. Magnetic fields allow magnets to interact without touching.

17 Magnetic Field Lines Magnetic field lines spread out from one pole, curve around a magnet, and return to the other pole. The lines form complete loops from pole to pole and never cross. You can NOT see magnetic fields, but you can see its effects. Magnetic fields act in three dimensions.

18 Magnetic Field Lines

19 Magnetic Fields

20 Magnetic Field Lines

21 Magnetic Field Lines 3D

22 Magnetic Field Lines Like Poles

23 Magnetic Field Lines Unlike Poles

24 Magnetic Fields Demonstration of magnetic fields. Materials Bar Magnets Iron Filings Transparency Paper

25 Inside A Magnet The magnetic properties of a material depend on the structure of its atoms. All matter is made up of atoms. Protons p+ Neutrons neutral Electrons e- A moving electron produces a magnetic field. The spinning and orbiting motion of the electrons make each atom a tiny magnet.

26 Inside A Magnet In most materials, the magnetic fields of the atoms point in random directions which virtually cancels one another out. In certain materials, the magnetic fields of the spinning electrons of many atoms are aligned with one another. A cluster of billions of atoms that all have magnetic fields that are lined up in the same way is known as magnetic domain.

27 Magnetic Domains In a magnetized material all or most of the domains are arranged in the same direction.

28 Magnetic Domains

29 Magnetic Materials A material that shows strong magnetic effects is said to be a ferromagnetic material. ferrum-latin word for iron Common ferromagnetic materials: Iron Nickel Cobalt

30 Making Magnets Magnets used everyday are man-made. Made from ferromagnetic materials. Unmagnetized material is placed in a strong magnetic field or rubbed with one pole of a strong magnet. This causes the domains to line up in the same direction creating a magnet.

31 Making Magnets Some metals, such as the ordinary steel that paper clips are made of, are easy to magnetize but lose their magnetism quickly. Materials that lose their magnetism quickly are called temporary magnets.

32 Making Magnets Harder metals are more difficult to magnetize but tend to stay magnetized. A magnet made up of material that keeps its magnetism is called a permanent magnet.

33 Question/Answer How does a magnet attract another object? The magnet s field causes the object to The magnet s field causes the object to become a magnet.

34 How Can You Destroy a Magnet? Drop it or strike it hard. Causes the domains to be knocked out of alignment. Heat it. What happens to particles in a solid when you heat them? They vibrate faster and more randomly thus making it more difficult for the domains to stay in alignment.

35 Breaking Magnets No matter how many times a magnet is cut in half, each piece retains its magnetic properties.

36 Breaking Magnets

37 Detecting Fake Coins Activity Can you use a magnet to tell the difference between fake and real coins? Materials Needed: Various coins Metric ruler Coin-sized steel washers Small bar magnet Thin cardboard Popsicle Stick Pencil Tape Protractor

38 What is a compass? Compass-a device that has a magnetized needle that can spin freely. The compass needle usually points north. Why? Let s find out!

39 Late 1500 s Earth As A Magnet Sir William Gilbert English physician Confirmed that a compass always points north but no one knew why. Gilbert suggested that a compass always points north because the Earth acts as a magnet.

40 Earth As A Magnet Earth has an immense magnetic field surrounding it, just as there is a magnetic field around a bar magnet. Gilbert believed that the center of the Earth contained magnetic rock scientists now believe that this is NOT the case.

41 Earth As A Magnet Scientists believe that the Earth s core is too hot for it to be a solid. Scientists do know that the Earth s magnetism is created by the circulation of molten metal (iron and nickel) within the Earth s core. The poles on a magnetized needle align themselves with the magnetic field of the Earth.

42 Magnetic Declination Earth s magnetic poles are not the same as the geographic poles. The magnetic north pole (in northern Canada) is about 1,250 kilometers from the geographic north pole. The geographic north pole is sometimes called true north. The magnetic south pole is located near the coast of Antarctica.

43 Magnetic Declination Magnetic Declination-the angle between geographic north and the north to which a compass needle points. Magnetic declination changes over time because the magnetic poles move slowly. Between 1580 and 1820, the direction i of magnetic north in London changed by 35 degrees.

44 Magnetic Declination

45 Magnetic Declination in North America

46 The Magnetosphere Earth s magnetic field extends into space, which contains electrically charged particles. Earth s magnetic field affects the movements of electrically charged particles in space. Charged particles also affect Earth s magnetic field.

47 The Magnetosphere Between 1,000 and 25,000 kilometers above Earth s surface are two doughnut-shaped regions called the VanAllenbelts. Discovered by J.A. Van Allen These regions contain electrons and protons traveling at very high speeds.

48 Van Allen Belts

49 Van Allen Belts

50 The Magnetosphere Other electrically charged particles in space come from the sun. Earth and the other planets experience a solar wind.

51 The Magnetosphere Solar wind-a stream of electrically charged particles flowing at high speeds from the sun. The solar wind pushes against Earth s magnetic field, and surrounds the field.

52 The Magnetosphere

53 The Magnetosphere The region of Earth s magnetic field shaped by the solar wind is called the magnetosphere. The solar wind constantly reshapes the magnetosphere as Earth rotates on its axis.

54 The Magnetosphere Most particles in the solar wind do not penetrate the Earth s magnetic field; however, some do. These particles follow the lines of Earth s magnetic field to the magnetic poles. At the poles the magnetic field lines dip down to Earth s surface.

55 The Magnetosphere When charged particles get close to Earth s surface, they interact with atoms in the atmosphere. This causes one of the Earth s most spectacular displays auroras. auroras

56 Aurora In the northern hemisphere, an aurora is called the Northern Lights aurora borealis. In the southern hemisphere, an aurora is called the Southern Lights aurora australis.

57 Aurora borealis Northern Lights

58 Aurora borealis Northern Lights

59 Aurora australis Southern Lights

60 Aurora australis Southern Lights

61 Effects of Earth s Magnetic Field Since Earth produces a strong magnetic field, Earth itself can make magnets. Earth s magnetic field acts on rocks that contain magnetic material rocks on the ocean floor. The ocean floor is produced from molten material that seeps up through h a long crack in the ocean floor, known as the mid-ocean ridge.

62 Earth Leaves a Record When the rock is molten, the iron it contains lines up in the direction of Earth s magnetic field. As the rock cools and hardens, the iron is locked in place. This creates a permanent record of the magnetic field.

63 Earth Leaves a Record Scientists have discovered that the direction and strength of Earth s magnetic field has changed over time. Earth s magnetic poles periodically reverse themselves. This last happened 780, years ago.

64 Earth Leaves a Record Earth s magnetic field arises from the motion of molten metal in Earth s core. Changes in the flow of that metal result in changes in Earth s magnetic field.

65 Earth Leaves a Record Paleomagnetism-the natural remnant magnetism in rock bodies; the permanent magnetization acquired by rock that t can be used to determine the location of the magnetic poles at the time it became magnetized. Normal polarity-a magnetic field that is the same as that which exists at present. Reverse polarity-a magnetic field opposite to that which exists at present.