Magnetic Forces and Compasses

When magnets are placed in the vicinity of other magnets, they align as shown below:

This property underlies how a compass works. The Earth has a magnetic field which acts as if there is a large magent buried deep within the Earth. The field has average strength 0.00005 Tesla. This is a weak magnetic field; magnetic fields on the Sun range from 0.0001 to 0.3 Tesla or so while the fields in MRI machines are on the order of several Tesla. The field emerges and enters the Earth near Canada and between Australia and Antarctica. When other mangets (compasses) are placed in the Earth's magnetic field, they align pointing toward the magnetic pole of the Earth (which is different from the true North pole of the Earth).

The Earth's magnetic field changes polarity every 100,000 to 1,000,000 years. on avearge every 450,000 years. The reversals are quick generally taking 1,000 to 10,000 years. The last reversal occurred 780,000 years ago. However, there is evidence from Steens Mountain in Oregon, that the field switched at a rate of 6 degrees per year around 15 million years ago. The north end of a compass (the magnet) points toward the North magnetic pole of the Earth (which is actually the South magnetic pole, at the present time).