Magnetic fields surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges. The magnetic field, at a given point, is specified by both a direction and a magnitude (or strength); as such it is a vector field.

In special relativity, the electric field and magnetic field are two interrelated aspects of a single object, called the electromagnetic field. A pure electric field in one reference frame is observed as a combination of both an electric field and a magnetic field in a moving reference frame.

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