Figure 132.
MAGNETIC FIELD AND CURRENTS What you have learned so far is that currents and magnetism are related. Currents themselves can create a significant magnetic field as can be demonstrated by trying to use a compass near overhead electric power lines. Current loops create magnetic fields, as has been demonstrated in the way motors work. What about a straight wire and the current applied to it? Will this cause a significant electric field. Look back at figure 127. It shows the direction of the magnetic field as it applies to a wire and a current. This is referred to as the right-hand rule two. The current will wrap around counterclockwise if the current is going upward as is identified by the curvature of the fingers and the direction of the thumb. For a long, straight wire with a current applied, the magnitude of the magnetic field B will be proportional to the current inversely proportional to r, which is the shortest distance to the wire. The actual equation is shown in figure 133. It involves a constant called the permeability of free space, which is related to the speed of light. The assumption is that the wire is very long with the constant being four pi x 10-7 Teslameters per ampere.
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