Ch 27 Magnetic Field and Forces

Ch 27 Magnetic Field and Forces - Electrons produce two...

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Electrons produce two kinds of magnetism: Electron spin and electron revolution . Electrons spin about their own axis like tops, and they also “revolve” around the nucleus of the atom. In most common magnets, electron spin is the main contributor to magnetism. Every spinning electron is a tiny magnet.
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A pair of electrons spinning in the opposite direction cancel out their magnetic field . This is why most substances are not magnetic. In substances like iron, nickel and cobalt the fields do not cancel out. Each atom has 4 electrons whose spin magnetism is not cancelled. Most of the iron objects you are familiar with are magnetized to some degree : filing cabinets, refrigerators, even cans of food. Pass a compass over these objects and see.
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Several grains of Nd Fe B with magnetic domains made visible via contrast with a Kerr-microscope. The magnetic field of a single iron atom is so strong cause adjacent iron atoms to align into magnetic domains .
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Each domain is perfectly magnetized and made up of billions of aligned atoms . Domains are microscopic. There are many domains in crystal iron. However, not every piece of iron is a magnet, because the domains themselves are not aligned. Another magnet can align domains to make a magnet. Tapping can also help align these domains. If a magnet is dropped or heated domains can become jostled to make the magnet weaker.
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Un-magnetized Material Magnetized Material
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Electric Currents and Magnetic Fields It is of fundamental fact that a moving charge causes a magnetic field . Hence a current produces a magnetic field. The magnetic field around a current carrying wire can be measure by placing compasses around the wire. It is found that the magnetic field produces concentric circles around the wire having the same strength of magnetic B-fields .
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Any charge moving through a magnetic field experiences a magnetic force . That force grows stronger the faster the particle moves through the field. And also the stronger is the magnetic field the larger the magnetic force acts on a charge particle .
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Since a single charge moving creates a magnetic field , a lot of particles creates a bigger magnetic field. A current in a straight wire produces concentric rings of electric fields.
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Magnetic field around a long current carrying wire.
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THE MAGNETIC FIELD CAUSED BY THE CURRENT LOOP The magnetic field-lines form rings around the conductors. Magnetic field of a long straight wire
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Magnetic Fields More formal Investigation To understand a magnetic field it is easier to recall how an electric field was understood in previous chapters . 1) A distribution of electric charge at rest creates an electric field E in the surrounding space. 2) The electric field exerts a force F = q E on any charge that is present in the field.
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