The Magnetic Field

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The Magnetic Field

In the world of electromagnetics, there are two main types of fields. The Electric Field arises due to electric charge. Suppose now that the electric charges are moving. The flow of electric charge is known as electric current, and is measured in Amperes [A]. It turns out that electric current produces a Magnetic Field (H-field). Unlike the Electric Field which points towards or away from electric charge, the magnetic field encircles electric current, as shown in Figure 1:

the H-field (magnetic field) encircles flowing electric current

Figure 1. The Magnetic Field (H-Field) Encircles an Electric Current.

In Figure 1, the current and magnetic field obey the right-hand rule. If your thumb points in the direction of the current, then your right hand fingers will wrap around in the direction of the magnetic field.

Electric Current is the flow of charge, measured in Amperes (Amps) and typically written I. One Amp is equivalent to 1 Coulomb per second. If I Amps are flowing through a straight wire, the magnetic field that surrounds the wire a distance R from the wire is given by:

magnetic field
[Equation 1]

Equation [1] states that the magnitude of the magnetic field decreases with distance as 1/R from the wire. The Magnetic field is also directly proportional to the current I. The Magnetic field is a vector quantity like the Electric Field. The magnitude of the magnetic field is given by Equation [1] and the direction doesn't point away, towards, or in the same direction as the wire, but wraps around the wire.

The units for the Magnetic Field are Amps/meter [A/m].

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