THE MAGNETIC FIELD!
There are two sources for B
fields, namely fundamental point particles (like the electron),
which have intrinsic magnetic fields, and charges of any kind
moving with respect to the observer. The ancient Greeks
noticed that there were metallic rocks that were naturally
magnetic... lodestones, or permanent magnets. Each such
natural magnet has two poles, North and South.
The direction of the vector field B
at a certain location is the direction a compass needle would
point, at that location.

Magnetic
field lines ALWAYS form closed loops! 
The Lorentz Force, F =
qvBsinθ. The vector F, and the plane containing
v and B are always at right angles to one
another.
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