PHY213_Chapter19_Sec1to5

PHY213_Chapter19_Sec1to5 - Chapter 19 Magnetism Magnetic...

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Chapter 19 Magnetism
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General Physics Magnetic Fields I Sections 1–5
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General Physics First Observations – Greeks Observed electric and magnetic phenomena as early as 700 BC Found that amber, when rubbed, became electrified and attracted pieces of straw or feathers Also discovered magnetic forces by observing magnetite attracting iron
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General Physics Magnets Polesof a magnet are the ends where objects are most strongly attracted Two poles, called north and south For example – bar magnet Like poles repel each other and unlike poles attract each other Similar to electric charges Magnetic poles cannot be isolated If a permanent magnetic is cut in half repeatedly, you will still have a north and a south pole—two poles or a dipole Thus far, single magnetic poles or monopoles have not been detected This differs from electric charges—single isolated charges do exist and have been detected
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General Physics More About Magnetism An unmagnetized piece of iron can be magnetized by rubbing it with a magnet Somewhat like rubbing an object to charge an object Magnetism can be induced If a piece of iron, for example, is placed near a strong permanent magnet, it will become magnetized Soft magnetic materials, such as iron, are easily magnetized They also tend to lose their magnetism easily Hard magneticmaterials, such as cobalt and nickel, are more difficult to magnetize They tend to retain their magnetism
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General Physics Sources of Magnetic Fields A magnetic field surrounds a properly magnetized magnetic material The region of space surrounding a moving charge includes a magnetic field The charge will also be surrounded by an electric field
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General Physics Magnetic Fields A vector quantity Symbolized by Direction is given by the direction a north poleof a compass needle points in that location Magnetic field linescan be used to show how the field lines, as traced out by a compass, would look B
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General Physics Magnetic Field Lines, sketch A compass can be used to show the direction of the magnetic field lines (left) A sketch of the magnetic field lines (right) Active Figure: Magnetic Field of a Permanently Magnetized Bar
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General Physics Magnetic Field Lines, Bar Magnet Iron filings are used to show the pattern of the magnetic field lines The direction of the field is the direction a north pole would point
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This note was uploaded on 08/25/2009 for the course PHY 213 taught by Professor Cao during the Summer '08 term at Kentucky.

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PHY213_Chapter19_Sec1to5 - Chapter 19 Magnetism Magnetic...

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