Answer: The
needle of a compass is a small magnet, one that is allowed to pivot in
the horizontal plane. The needle experiences a torque from the ambient
magnetic field of the Earth. The reaction to this torque is the needle’s
preferred alignment with the horizontal component of the geomagnetic field.
The ‘north’ end of the compass needle is simply the north
end of the magnet, and it is the end of the compass needle that points
in the general direction of the geographic north pole; naturally, the
‘south’ end of the compass needle is the south end of the
magnet and it points in the opposite direction, towards the general direction
of the geographic south pole. Having said this, the preferred directionality
of a compass can be affected by local perturbations in the magnetic field,
like those set up by (say) a near-by electrical system; a compass can
also be affected by local magnetization of the Earth's crust, particularly
near large igneous or volcanic rock deposits. |