L06_electromagnets7 - Electromagnets Name: Teammates:...

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Electromagnets Name: Teammates: Introduction Mankind’s knowledge of magnetism is nothing new; people have known of its existence for millennia. The term “magnet” comes from the ancient Greece word “Magnesia”, which is the place in Thessaly where the naturally occurring magnetic rock lodestone was found in the BCE era. However, the ability to create magnetism is a much more recent phenomenon. In 1820, Hans Oersted discovered that he could deflect the needle of a compass by running a current through a nearby wire. He deduced that the reason for this was because the current was producing its own magnetic field. This led to the discovery of electromagnets. A typical electromagnet is made by coiling conducting wire around a ferromagnetic core. One typical coiling method is what is often referred to as the solenoid. Solenoids The magnetic field created by a single wire is given by: o I B 2r µ = π⋅ where µ o is the permittivity of free space (4 π x 10 -7 Tm/A) and r is the distance for the wire. The equation shows that currents on the order of 1-100 amps produce fairly weak fields outside of a few millimeters from the wire. One way to boost the field from a wire is to add together the effect of many wires that are all carrying current in the same direction. This is the basis behind a solenoid, a wire that is coiled into a series of loops that are all laid on top and next to one another. In the middle of the solenoid, the magnetic fields from all of the wire loops add vectorally to provide a very strong field that is parallel to the axis of the solenoid. When the wires are close together, and the solenoid diameter is not too large, the magnetic field within the solenoid can be approximated by a uniform field given by B = µ nI where µ is the permitivity of the material contained in the solenoid (if there is something other than air in it), n is the number of wire loops per unit length, and I is the current running through the solenoid. If a vacuum (or air) exists within the solenoid, then the permitivity is that of free space, i.e. µ = µ o .= 4 π x 10 -7 Tm/A From this equation, we see that we can change the magnetic field by varying the number of turns per unit length, the current running through the solenoid, or by placing a different type of material, like iron core, in the solenoid.
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L06_electromagnets7 - Electromagnets Name: Teammates:...

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