are: a means of representing a magnetic field using directed curves (i.e. curves with arrows on them). [P4.2]
are drawn: so that at any point the magnetic field is tangential to the line and points in the direction indicated by the direction of the field line. [P4.2]
therefore are directed: away from north magnetic poles and towards south magnetic poles. (This direction is that in which the north pole of a freely suspended compass needle would point - which means of course that the north geographical pole of the Earth is actually a south magnetic pole!) [P4.2]
have spacing: which is related to the magnitude of the magnetic field, i.e. where the lines are close together the field is strong and where they are further apart the field is weaker. [P4.2]
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