5. Magnetostatics

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5. Magnetostatics
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Early evidence for the magnetic field.
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Magnetic Field
Bar magnet
Magnetic field lines
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Magnetic Field of the Earth
Direction measured by a compass.
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Oersted, in 1820
What he saw.
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Qersteds experiment, modern version
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Biot and Savert found that the force on a compass
encircles a wire. Formulated the Biot-Savert law.
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Ampere stated that all magnetic field are
generated by currents. The elementary magnetic
dipoles are current loops.
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How does the field act on the moving charge?
How is the field generated by the moving charges?
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Lorentzs law
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Example 5.2 Cyclotron Motion
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Cloud Chamber
1.6 MeV proton
7 MeV alpha
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The Cylcotron
O. E. Lawrence M. S. Livingston 1934
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Magnetic Bottle
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Van Allen Belts
Protons and electrons from the solar wind are
trapped by the earths magnetic field.
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Currents
Line current I
1 A 1 C/s
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Magnetic forces do not work!
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Example 5.3
B points into the page.
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Surface current density
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Volume current density
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Example 5.4
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Biot-Savart Law
Magnetostatics Steady currents
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Example 5.5
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Example 5.6
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Superposition principle for the magnetic field
gives the different versions of the Biot-Savart
law.