A simple rule allows the prediction of the field direction if the direction of electron motion is known: If the wire is encircled by the fingers of one's left hand, with the thumb pointing in the direction of electron motion, the magnetic field lines encircle the wire in the same direction as the fingers, and a compass needle will align itself tangent to these lines.
(A simple rule; allows; the prediction of the field direction) Context(A simple rule allows,List([0, 20))):(the magnetic field lines; encircle; the wire) (a compass needle; will align; itself; tangent to these lines) (the direction of electron motion; is known; ) (the wire; is encircled; by the fingers of one's left hand) (the thumb; pointing; in the direction of electron motion)
A simple rule allows,List([0, 20))
A simple rule the magnetic field lines a compass needle the direction of electron motion the wire the thumb
allows encircle will align is known is encircled pointing
the prediction of the field direction
the wire
itself tangent to these lines
by the fingers of one's left hand
in the direction of electron motion