Lesson_4.1_Printable_PPT

Lesson_4.1_Printable_PPT - Magnets and magnetic poles The...

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Magnets and magnetic poles The ancient Greeks, originally those near the city of Magnesia, and also the early Chinese knew about strange and rare stones called lodestone with the power to attract iron. This property later came to be known as magnetic property. steel needle stroked with such a stone became Soon magnetic compass became an essential tool for navigation. A steel needle stroked with such a stone became "magnetic" as well, and about 1000 years ago the Chinese found that such a needle, when freely suspended, pointed north-south.
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A freely suspended magnet always comes to rest in the north-south direction The end pointing north is called the north pole (N) The end pointing south is called the south pole (S) The north pole and south pole of a magnet are similar to the positive and negative charges in electricity. Materials that are attracted by a magnet are called magnetic materials .
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Interaction between magnetic poles Just like electric charges, magnetic poles interact in such a way that: 1. Like poles repel. A north pole repels a north pole, a south pole repels a south pole. N N S S 2. Unlike poles attract. A north pole attracts a south pole.
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But unlike electric charges, magnetic poles do not exist freely. If a magnet is divided into many thousands of small pieces, each piece will be a magnet with a north pole and a south pole. The smallest part of a magnet consists of a north pole and a south pole and is called a magnetic dipole. All magnetic materials are made up of dipoles. A magnetic monopole doesn’t exist. If at all it exists, it hasn’t been detected yet.
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Magnetic Field A magnetic filed is a three dimensional space around a magnet where it exerts force on other magnets. A magnetic filed around a magnet can be studied using the concept of field lines . A field line is the path taken by a test pole placed near a magnet. A standard test pole is a unit north pole . A unit north pole placed near a bar magnet moves away from its north pole towards the south pole.
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Magnetic field lines originate at the north pole and end at the south pole. Magnetic field lines that describe a magnetic filed are similar to electric field lines that describe an electric field. The magnetic field lines of a bar The path taken by the unit test pole is called a field line . magnet can be traced out with the use of a compass as shown in the figure. http://www.walter-fendt.de/ph11e/mfbar.htm Magnetic field is represented by B and is measured in a unit called tesla ( T ) A common unit used for measuring magnetic field is the gauss (G). 1 G = 10 -4 T
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Magnetic Field due to Electric Current If a compass needle is kept below a conducting wire that carries an electric current, the compass needle deflects indicating the presence of a magnetic field.
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The direction of the magnetic field is given by the right hand rule. If you wrap the four fingers of
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Lesson_4.1_Printable_PPT - Magnets and magnetic poles The...

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