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# chapter29notes - Chapter 29 Magnetic Fields Today Magnetism...

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1 Chapter 29 •Magnetic Fields Today: • Magnetism and Magnetic Field Electric Current and Magnetism • Magnetic Forces on Electric Current

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2 Magnetism • What are magnets? – Objects with two poles, north and south poles • The pole that points to geographical north is the north pole and the other is the south pole – Principle of compass – These are called magnets due to the name of the region, Magnesia, where rocks that attract each other were found • What happens when two magnets are brought to each other? – They exert force onto each other – What kind? – Both repulsive and attractive forces depending on the configurations • Like poles repel each other while the unlike poles attract
3 Magnetism • So the magnet poles are the same as the electric charge? – No. Why not? – While the electric charges (positive and negative) can be isolated the magnet poles cannot be isolated. – So what happens when a magnet is cut? • If a magnet is cut, two magnets are made. • The more they get cut, the more magnets are made – Single pole magnets are called the monopole but it has not been seen yet • Ferromagnetic materials: Materials that show strong magnetic effects – Iron, cobalt, nickel, gadolinium and certain alloys • Other materials show very weak magnetic effects

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4 – The direction of the magnetic field is tangent to a line at any point – The direction of the field is the direction the north pole of a compass would point to – The number of lines per unit area is proportional to the strength of the magnetic field – Magnetic field lines continue inside the magnet – Since magnets always have both the poles, magnetic field lines form closed loops unlike electric field lines Magnetic Field Just like the electric field that surrounds electric charge, a magnetic field surrounds a magnet What does this mean? – Magnetic force is also a field force – The force one magnet exerts onto another can be viewed as the interaction between the magnet and the magnetic field produced by the other magnet – What kind of quantity is the magnetic field? Vector or Scalar? So one can draw magnetic field lines, too. Vector
5 Earth’s Magnetic Field • What magnetic pole does the geographic north pole has to have? – Magnetic south pole. What? How do you know that? – Since the magnetic north pole points to the geographic north, the geographic north must have magnetic south pole • The pole in the north is still called geomagnetic north pole just because it is in the north – Similarly, south pole has magnetic north pole • The Earth’s magnetic poles do not coincide with the geographic poles b magnetic declination – Geomagnetic north pole is in northern Canada, some 1300km off the true north pole • Earth’s magnetic field line is not tangent to the earth’s surface at all points – The angle the Earth’s field makes to the horizontal line is called the angle dip

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6 Electric Current and Magnetism • In 1820, Oersted found that when a compass needle is
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chapter29notes - Chapter 29 Magnetic Fields Today Magnetism...

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