When might a compass NOT work properly?

Answer 1

A magnetic compass will not work near a magnet or any magnetic object.

A magnetic compass doesn't work near the magnetic dip poles -- near Earth's local north magnetic poles or near Earth's south magnetic pole.

Answer 2

There is no "why", because compasses work just fine at the north and south geographic poles.

The only trick is knowing exactly what geographic location they're pointing to.

At the north geographic (spin) pole, the compass always points exactly south, since EVERY direction from there is south. Also, at the north pole, the dip angle of the magnetic attraction is so steep that you'll have to have your instrument inclined from horizontal.

The magnetic south pole on the other hand, is thousands of km north of the geographic (spin) pole. So, at the south geographic (spin) pole, your compass will behave as you're accustomed to. It points north, since EVERY direction from there is north, and it points toward the Earth's south magnetic pole,

which really may not help you too much in that situation.

The Earth's magnetic field is caused by electric currents generated in the magma, and as these masses move, so do the poles.

Answer 3

The magnet stuck to it. Stray magnetic fields. A large motor or generator nearby.

Answer 4

Of course a compass will work at the equator -or anywhere else, come to that. It always aligns itself with the earth's magnetic field.