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Physics214Week12

Physics214Week12 - This Week Magnetism Are you attracted or...

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This Week Magnetism: Are you attracted or repulsed? Where does magnetism come from? What use is magnetism? Post pictures and notes on refrigerators Electrical motors turn electricity into work Generators turn heat energy into electricity Transformers for power transmission and Ipod. Earths Magnetic field. Northern lights. 12/09/11 Physics 214 Fall 2011 1

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12/09/11 Physics 214 Fall 2011 2 Magnetism Electric charge is also responsible for the force that we call magnetism. Moving charge, that is a current, produces a force field which we term the magnetic field B. Since atoms contain “moving charge” most atoms and substances have magnetic behavior. In the case of iron this effect is very strong.
12/09/11 Physics 214 Fall 2011 3 Magnetic field There are differences between the electric field and the magnetic field. A magnet has two poles and a magnetic monopole has never been observed. The field lines are continuous loops Like poles repel and unlike poles attract A magnetic field only acts on moving charge The force is perpendicular to the velocity so the moving charge is accelerated but does not gain or lose energy By definition the field lines enter a south pole and leave a north pole http://www.physics.purdue.edu/class/applets/phe/mfbar.htm

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12/09/11 Physics 214 Fall 2011 4 Earth’s magnetic field The earth has a dipole field inclined at 11 degrees to the axis of rotation. The North Pole (Arctic) is actually a magnetic south pole. It is thought that the field is produced by circulating electric currents in the molten iron core .
12/09/11 Physics 214 Fall 2011 5 Form of the force The force a charged particle moving with velocity v in a magnetic field B is given by F = qv perpendicular B or F = qvB perpendicular This means the maximum force is when v is at right angles to B and that the force is zero if v is parallel to B or v = 0. For a current in a wire qv = qL/t = IL so the force on a current carrying wire of length L is F = ILB perp Units of B are tesla (N x sec/coulombs x meters) (N/amps.meters) http://www.physics.purdue.edu/class/applets/phe/lorentzforce.htm

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12/09/11 Physics 214 Fall 2011 6 Fields from currents A current carrying wire produces circular field lines. Looking along the direction of the current the field lines are clockwise A current loop produces a dipole field A solenoid can produce a strong uniform field in a volume with small leakage. If it is placed in an iron cylinder the field is stronger and more contained http://www.physics.purdue.edu/class/applets/phe/mfwire.htm
Physics 214 Fall 2011 7 Force between two infinite wires If the two wires are very long then each wire sits in a B field which is at right angles to the wire. F/L = 2k’ I

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Physics214Week12 - This Week Magnetism Are you attracted or...

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