Thursday, 17 May 2012

How does a compass detect north?

A compass is a navigational instrument. It is used for determining the direction relative to the earth’s magnetic poles.

A compass consists of a magnetized pointer which is usually marked on the north end. This magnetized pointer is free to align itself with the earth’s magnetic field.

A compass needle will always point north no matter which way you spin. Since the needle is a magnet it knows where to point. A magnet pulls other magnet towards itself. The earth’s magnetic field stems from its molten metallic core. Each of the earth’s poles pulls on one end of the compass needle. This causes it to point in a direction that causes it to point in a direction that shows us where north direction is.

Generally compass are sealed instrument having a magnetized bar or needle turning freely upon a pivot or moving in a fluid. The compass was invented in ancient china sometime before the 2nd century. However, it was used for navigation only by the 11th century.

When we think of the North Pole, we usually think of the geographical North Pole. But that is not where a compass needle points. The earth’s magnetic field has a separate north pole. It is the point where the magnetic field lines become vertical and enter the earth and moves gradually with time. This point is currently somewhere off western Greenland, near Canada. The needle of a compass always aligns itself with the magnetic field lines. Hence, it points towards the magnetic north pole.


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