Magnetism

=//**Magnetism** // =

**Essential Questions:**
**1. What makes something magnetic?  2. What are the properties of a magnet?  3. What are magnetic field lines? **

What Makes Something Magnetic?
A magnet is an object or material that attracts certain metals, such as iron, nickel and cobalt. It can also attract or repel another magnet. All magnets have North-seeking (N) and South-seeking (S) poles. When magnets are placed near each other, opposite poles attract and like poles repel each other. Various electrical devices make use of magnets.

There are three main types of magnets: 1. Permanent magnets 2. Temporary magnets 3. Electromagnets

Permanent magnets are those we are most familiar with, such as the magnets hanging onto our refrigerator doors. They are permanent in the sense that once they are magnetized, they retain a level of magnetism. As we will see, different types of permanent magnets have different characteristics or properties concerning how easily they can be demagnetized, how strong they can be, how their strength varies with temperature, and so on.
 * Permanent Magnets**

Temporary magnets are those which act like a permanent magnet when they are within a strong magnetic field, but lose their magnetism when the magnetic field disappears. Examples would be paperclips and nails and other soft iron items.
 * Temporary Magnets**

An electromagnet is a tightly wound helical coil of wire, usually with an iron core, which acts like a permanent magnet when current is flowing in the wire. The strength and polarity of the magnetic field created by the electromagnet are adjustable by changing the magnitude of the current flowing through the wire and by changing the direction of the current flow.
 * Electromagnets**

[[file:magnets.ppt]]
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Magnets always have two poles, come in various shapes, and attract or repel other magnets.

__**Names of poles **__
 All magnets have a North-seeking pole (N) and South-seeking pole (S). In a compass, the side marked (N) will point toward the Earth's North magnetic pole. Thus, it is called the "North-seeking pole." Also note that the Earth's North magnetic pole is not the same thing as the North Pole. They are actually several hundred miles apart.

__Various shapes __
 The magnet can be made into various shapes. The bar magnet is the most common configuration. Bar magnet  Magnets also can be square, spherical, shaped like a horseshoe, and even shaped like a donut. Horseshoe magnet <span style="font-family: 'Arial Black',Gadget,sans-serif;">If you put an iron plate across the N and S poles of a horseshoe magnet, that would essentially "short circuit" the effect of the magnetism, such that its strength would not be very great. As soon as the plate was removed, the magnet would regain its full strength. That method is sometimes used in magnets that are temporary to help keep their magnetic properties for a longer time.

__<span style="font-family: 'Arial Black',Gadget,sans-serif;">Cutting a magnet __
<span style="font-family: 'Arial Black',Gadget,sans-serif;"> An interesting characteristic of magnets is that when you cut a magnet into parts, each part will have both N and S poles.

<span style="font-family: 'Arial Black',Gadget,sans-serif;">__Attraction and<span style="font-family: 'Arial Black',Gadget,sans-serif;"> repulsion__
<span style="font-family: 'Arial Black',Gadget,sans-serif;"> Magnets strongly attract iron, nickel and cobalt, as well as combinations or alloys of these metals. Also, unlike poles of two magnets will attract, but like poles will repel. Thus, N and S attract, while S and S will repel each other.



What are Magnetic Field Lines?
<span style="font-family: 'Comic Sans MS',cursive;">Magnetic fields are created by moving electric charge. Magnets have a north and south pole. A magnetic field is defined by the lines of force that go from the north to the south pole. The illustration to the right shows the imaginary field lines coming out of one pole and going into the other (click on the illustration for a VRML model of the field lines). Things that are naturally magnetic are magnetic because of the orientation of the moving electrons orbiting the nuclei in the atoms. Electromagnets are metals that become magnetic when a coil of wire with a electric current is wrapped around it. The current in the wire induces a magnetic field in the metal.

Magnetic fields in turn can also create electricity. For example, a rotating magnet can induce an electric current in a piece of wire. This is how many power plants operate. In a coal, oil, or nuclear power plant, water is heated and becomes steam, which is used to turn turbines. In a hydroelectric plant, water from a dam or waterfall is used to turn the turbines. These turbines spin magnets which create the electricity for your home.

Properties of the magnetic lines of force

 * 1) <span style="font-family: 'Comic Sans MS',cursive;">The magnetic lines of force originate from the North Pole of a magnet and end at its South Pole.
 * 2) <span style="font-family: 'Comic Sans MS',cursive;">The magnetic lines of force come closer to one another near the poles of a magnet but they are widely separated at other places.
 * 3) <span style="font-family: 'Comic Sans MS',cursive;">The magnetic lines of force do not intersect (or cross) one another.
 * 4) <span style="font-family: 'Comic Sans MS',cursive;">When a magnetic compass is placed at different points on a magnetic line of force, it aligns itself along the tangent to the line of force at that point

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<span style="font-family: Verdana,Geneva,sans-serif;">Applications:
<span style="font-family: Verdana,Geneva,sans-serif;"> There are numerous applications of magnets.

<span style="font-family: Verdana,Geneva,sans-serif;">Creating a magnet
<span style="font-family: Verdana,Geneva,sans-serif;"> You can magnetize a piece of steel by rubbing a magnet in one direction along the steel. This lines up the many of the domains or sections of aligned atoms in the steel, such that it acts like a magnet. The steel often won't remain magnetized for a very long time, while the true magnet is "permanently" magnetized and retains its strength for a long time. If you use soft iron or steel, such as a paper clip, it will lose its magnetism quickly. Also, you can disorient the atoms in a magnetized needle by heating it or by dropping the needle on a hard object.

<span style="font-family: Verdana,Geneva,sans-serif;">Compass
<span style="font-family: Verdana,Geneva,sans-serif;"> The first true application of a magnet was the compass, which not only helps in navigation by pointing toward the North magnetic pole, but it is also useful in detecting small magnetic fields. A compass is simply a thin magnet or magnetized iron needle balanced on a pivot. The needle will rotate to point toward the opposite pole of a magnet. It can be very sensitive to small magnetic fields.

<span style="font-family: Verdana,Geneva,sans-serif;">Other uses
<span style="font-family: Verdana,Geneva,sans-serif;"> Magnets are found in loudspeakers, electrical motors and electrical generators. A very common application of magnets is to stick things to the refrigerator. Since the outer shell of most refrigerators is made of steel, a magnet will readily stick to it. The type of magnets used often consists of a thin sheet of a magnetic material.

<span style="font-family: 'Arial Black',Gadget,sans-serif;">How do I read a compass?
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Resources:
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[|http://my.execpc.com/~rhoadley/magtypes.htm]

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