MAGNETIC FIELDS

==Magnetic Fields== A magnetic field is the magnetic effect of electric currents and magnetic materials. Magnetic fields are most often encountered as a force created by permanent magnets or by moving charges, which pull on ferromagnetic materials such as iron, cobalt, or nickel, and attract or repel other magnets. They also apply a force to moving charges. Magnetic fields are '''Non Divergent''' which means that they have a definite start and stop point. The field lines are defined as starting from the North pole and ending at the South pole. [image:http://i.imgur.com/TkGaJSG.png] Common magnetic field configurations are shown below. [image:http://i.imgur.com/W3wRRJg.gif] ==The Earth's Magnetic Field== The Earth's magnetic field is similar to that of a bar magnet tilted 11 degrees from the spin axis of the Earth. The problem with that picture is that the Curie temperature of iron is about 770 C . The Earth's core is hotter than that and therefore not magnetic. So how did the Earth get its magnetic field? [image:http://i.imgur.com/WDc7IGH.jpg] Magnetic fields surround electric currents, so we surmise that circulating electic currents in the Earth's molten metalic core are the origin of the magnetic field. A current loop gives a field similar to that of the earth. The magnetic field magnitude measured at the surface of the Earth is about half a Gauss and dips toward the Earth in the northern hemisphere. The magnitude varies over the surface of the Earth in the range 0.3 to 0.6 Gauss. The Earth's magnetic field is attributed to a dynamo effect of circulating electric current, but it is not constant in direction. Rock specimens of different age in similar locations have different directions of permanent magnetization. Evidence for 171 magnetic field reversals during the past 71 million years has been reported. Although the details of the dynamo effect are not known in detail, the rotation of the Earth plays a part in generating the currents which are presumed to be the source of the magnetic field. Mariner 2 found that Venus does not have such a magnetic field although its core iron content must be similar to that of the Earth. Venus's rotation period of 243 Earth days is just too slow to produce the dynamo effect. Interaction of the terrestrial magnetic field with particles from the solar wind sets up the conditions for the aurora phenomena near the poles. [image:http://i.imgur.com/0dCrErM.jpg]