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Transcript of Reference Card, Assestment Card, Enrichment Card And

Reference Card, Assestment Card, Enrichment Card and Reference Card.

MagnetismThe ancient Greeks, originally those near the city of Magnesia, and also the early Chinese knew about strange and rare stones (possibly chunks of iron ore struck by lightning) with the power to attract iron. A steel needle stroked with such a "lodestone" became "magnetic" as well, and around 1000 the Chinese found that such a needle, when freely suspended, pointed northsouth. The magnetic compass soon spread to Europe. Columbus used it when he crossed the Atlantic ocean, noting not only that the needle deviated slightly from exact north (as indicated by the stars) but also that the deviation changed during the voyage. Around 1600 William Gilbert, physician to Queen Elizabeth I of England, proposed an explanation: the Earth itself was a giant magnet, with its magnetic poles some distance away from its geographic ones (i.e. near the points defining the axis around which the Earth turns).

The Magnetosphere

On Earth one needs a sensitive needle to detect magnetic forces, and out in space they are usually much, much weaker. But beyond the dense atmosphere, such forces have a much bigger role, and a region exists around the Earth where they dominate the environment, a region known as the Earth's magnetosphere. That region contains a mix of electrically charged particles, and electric and magnetic phenomena rather than gravity determine its structure. We call it the Earth's magnetosphere Only a few of the phenomena observed on the ground come from the magnetosphere: fluctuations of the magnetic field known as magnetic storms and substorms, and the polar aurora or "northern lights," appearing in the night skies of places like Alaska and Norway. Satellites in space, however,

sense much more: radiation belts, magnetic structures, fast streaming particles and processes which energize them. All these are described in the sections that follow.

More about the magnetosphere

But what is magnetism?Until 1821, only one kind of magnetism was known, the one produced by iron magnets. Then a Danish scientist, Hans Christian Oersted, while demonstrating to friends the flow of an electric current in a wire, noticed that the current caused a nearby compass needle to move. The new phenomenon was studied in France by Andre-Marie Ampere, who concluded that the nature of magnetism was quite different from what everyone had believed. It was basically a force between electric currents: two parallel currents in the same direction attract, in oposite directions repel. Iron magnets are a very special case, which Ampere was also able to explain.

What Oersted saw... In nature, magnetic fields are produced in the rarefied gas of space, in the glowing heat of sunspots and in the molten core of the Earth. Such magnetism must be produced by electric currents, but finding how those currents are produced remains a major challenge.

More about magnetism

Magnetic Field LinesMichael Faraday, credited with fundamental discoveries on electricity and magnetism (an electric unit is named "Farad" in his honor), also proposed a widely used method for visualizing magnetic fields. Imagine a compass needle freely suspended in three dimensions, near a magnet or an electrical current. We can trace in space (in our imagination, at least!) the lines one obtains when one "follows the direction of the compass needle." Faraday

called them lines of force, but the term field lines is now in common use.

Compass needles outlining field lines Fi eld lines of a bar magnet are commonly illustrated by iron filings sprinkled on a sheet of paper held over a magnet. Similarly, field lines of the Earth start near the south pole of the Earth, curve around in space and converge again near the north pole. However, in the Earth's magnetosphere, currents also flow through space and modify this pattern: on the side facing the Sun, field lines are compressed earthward, while on the night side they are pulled out into a very long "tail," like that of a comet. Near Earth, however, the lines remain very close to the "dipole pattern" of a bar magnet, so named because of its two poles.

Magnetic field lines from an idealized model. To Faraday field lines were mainly a method of displaying the structure of the magnetic force. In space research, however, they have a much broader significance, because electrons and ions tend to stay attached to them, like beads on a wire, even becoming trapped when conditions are right. Because of this attachment, they define an "easy direction" in the rarefied gas of space, like the grain in a piece of wood, a direction in which ions and electrons, as well as electric currents (and certain radio-type waves), can

easily move; in contrast, motion from one line to another is more difficult. A map of the magnetic field lines of the magnetosphere, like the one displayed above (from a mathematical model of the field), tells at a glance how different regions are linked and many other important properties.

More about magnetic field lines

Electromagnetic WavesFaraday not only viewed the space around a magnet as filled with field lines, but also developed an intuitive (and perhaps mystical) notion that such space was itself modified, even if it was a complete vacuum. His younger contemporary, the great Scottish physicist James Clerk Maxwell, placed this notion on a firm mathematical footing, including in it electrical forces as well as magnetic ones. Such a modified space is now known as an electromagnetic field. Today electromagnetic fields (and other types of field as well) are a cornerstone of physics. Their basic equations, derived by Maxwell, suggested that they could undergo wave motion, spreading with the speed of light, and Maxwell correctly guessed that this actually was light and that light was in fact an electromagnetic wave. Heinrich Hertz in Germany, soon afterwards, produced such waves by electrical means, in the first laboratory demonstration of radio waves. Nowadays a wide variety of such waves is known, from radio (very long waves, relatively low frequency) to microwaves, infra-red, visible light, ultra-violet, x-rays and gamma rays (very short waves, extremely high frequency). Radio waves produced in our magnetosphere are often modified by their environment and tell us about the particles trapped there. Other such waves have been detected from the magnetospheres of distant planets, the Sun and the distant universe. X-rays, too, are observed to come from such sources and are the signatures of high-energy electrons there.

-http://www-istp.gsfc.nasa.gov/Education/Imagnet.html-

INTRODUCTION TO THE MYSTERY OF MAGNETISM After reading this section you will be able to do the following:

Identify a number of common items that rely on magnetism to work.

Each time you turn on a light, listen to your stereo, fly in an airplane, or watch TV, you are depending on the principles of magnetism to work for you. Take a look at the pictures below. All of the items in these pictures have something to do with magnetism.

Hydroelectric Dam

Video Cassette Tape

Fan-

Magnetic Particle Inspection Unit

Airplane Navigational Panel Do you know how your life might be different without these? What do you think magnetism has to do with each of these things? Think about these

questions as you explore these materials on magnetism. We will revisit this page later. http://www.ndted.org/EducationResources/HighSchool/Magnetism/magnetismintro.htm

MAGNETIC PROPERTIES After completing this section you will be able to do the following:

Explain how small magnets can be while retaining its magnetic properties.

Questions 1. What is happening when you cut the magnet? 2. How small do you think you can make a magnet before it no longer acts like a magnet?

What is happening when you cut a magnet? A magnet can be cut into smaller and smaller pieces indefinitely, and each piece will still act as a small magnet. Thus, the cause of magnetism must be from a property of the smallest particles of the material, the atoms. So what is it about the atoms of magnets, or objects that can be magnetized (ferromagnetic materials), that is different from the atoms of other

material? For example, why is it that copper keys or aluminum soda cans cannot be magnetized?

AGNETIC PROPERTIES After completing this section you will be able to do the following:

Explain how small magnets can be while retaining its magnetic properties.

Questions 1. What is happening when you cut the magnet? 2. How small do you think you can make a magnet before it no longer acts like a magnet?

What is happening when you cut a magnet? A magnet can be cut into smaller and smaller pieces indefinitely, and each piece will still act as a small magnet. Thus, the cause of magnetism must be from a property of the smallest particles of the material, the atoms. So what is it about the atoms of magnets, or objects that can be magnetized

(ferromagnetic materials), that is different from the atoms of other material? For example, why is it that copper keys or aluminum soda cans cannot be magnetized?

REVIEW OF THE ATOM After completing this section you will be able to do the following:

Discuss the origin of magnetism. Discuss why some materials can be magnetized while others cannot.

The study of atoms, electrons, neutrons, and protons is so complex that throughout history scientists have developed several models of the atom. From the early Greek concept of the atom, about 2400 years ago, to today's modern atomic model, scientists have built on and modified existing models, as new information was discovered. There are still concepts on which scientists do not fully agree on. In an attempt