Lecture 32b - way ( domains ), making a strong net B-field....

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Magnetism in Matter
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2 Moving charges (currents) create B-fields. Where are the moving charges? Magnetism in matter arises from atomic current loops associated with orbiting and spinning electrons.
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Diamagnetic materials atoms are not permanent magnetic dipoles because the electrons are paired respond weakly to magnetic fields: they are repelled by magnets.
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4 In some materials the atoms are permanent magnetic dipoles but have random orientations. Superposition of B-field vectors over many atoms gives B=0 B B B B B
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Paramagnetic materials the atomic dipoles partially align with an external B field respond weakly to magnetic fields: they are attracted to magnets. Liquid oxygen is paramagnetic
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6 In Ferromagnetic materials (Fe, Ni, Co, some alloys containing these metals too), the atomic currents can all orient the same
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Unformatted text preview: way ( domains ), making a strong net B-field. B B B B 7 Sometimes the material is fragmented into many domains (top) and is thus unmagnetized. If the domains align (bottom) there is a net magnetic field (magnetized). 8 Aligning the domains of ferromagnetic material Randomly Oriented Magnetic Domains Magnetic Domains Aligned with External B-field. 9 i i Just like two loops of wire with current going in the same direction attractive force! 10 Opposite Poles attract. Similar Poles repel. This is not new physics. It is identical to the physics of our current loops. Now one can see why we can never break a magnet and get just one pole! 11 Demo magnetic shielding Ferromagnetic material has high magnetic permeability: it strengthens and redirects the external magnetic field....
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Lecture 32b - way ( domains ), making a strong net B-field....

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