點解南磁極放在指南針旁,指針會指住南磁極?

In a compass, the needle is in fact a small bar magnet. The North polarity (which is the "north seeking pole") moves along the direction of magnetic field lines, whereas the South polarity (the "south seeking pole") moves against the field line direction.

For a given "SOUTH magnetic pole"(南磁極), its associated magnetic field lines are pointing towards it and terminating on it. Thus when a compass is placed near the given "SOUTH magnetic pole", the compass needle aligns itself with the field lines with the North polarity of the needle moves in the direction of the magnetic field lines and South polarity in opposite direction to the field lines. This leads to the pointing of the needle towards the given "SOUTH magnetic pole".


2013-04-20 23:43:58 補充：
Be aware that the terms "North" and "South" in this context do not necessarily mean a "direction". They are only terms used to distinguish the two polarity of a bar magnet.

指南針顧名思義，指針只會指向南面(south pole)。
指南針指向北極係因為北極只係地理上既north pole，而事實上佢係south pole。