What is the essential effect of a magnetic field?

Answer:

A magnetic field is an imperceptible entity that exists in a region of space that may be void of all matter in the vicinity of a permanent magnet or an electric current. The magnetic field is a vector field an endless set of vectors one at each point in the region of space where the magnetic field exists. The affects of a magnetic field is either a permanent magnet or an electric current. The defining results of a magnetic field is to exert a torque on a magnetic dipole that is in the magnetic field as long as the magnetic dipole isn't parallel or anti-parallel to the magnetic field.