A magnetic compass is a simple navigational device that is used to determine direction. The needle in a magnetic compass will always point to the north, irrespective of location.

History

The magnetic compass was discovered by the Chinese, who used naturally occuring magnetic materials (lodestone) to navigate their ships. Initially a magnetic needle floating in a bowl of water was used as a compass. Later dry compasses with  a suspended magnetic needle were discovered.

Before the invention of the magnetic compass, sailors had to rely on the sun and other celestial objects for navigation.  With the advent of the compass, sailors had an independent method of finding the direction. Also, a compass can be used along with a sextant to determine the latitude. This increased the efficiency of marine expeditions and made them safer.

How a magnetic compass works

How a magnetic compass works

The core of the Earth has molten iron around some crystallized iron at the very center. The convection caused by the heat in the core and the rotation of the earth combine to make the liquid iron move in a rotational pattern. These rotational forces in the liquid iron layer produce weak magnetic fields around the spin axis of rotation.

The net result is that the Earth acts as if there is a giant bar magnet buried inside it, with the sound end of the magnet towards the North pole. The magnet is aligned slightly off center. As opposite poles of magnets attract, the magnetic compass needle always points towards the north. The field produced by the earth is very weak, which a very light needle that is freely suspended with almost frictionless bearings is needed in order to determine the direction.

Making a compass:

The materials needed to make a magnetic compass are:

• A bar magnet
• A needle
• A small piece of cork, styrofoam or light plastic
• A flat dish of water

First, you have to magnetize the needle. To do this, stroke one of the poles of the bar magnet along the length of the needle in the same direction around 20 times. Now, place the piece of cork in the dish of water so that it floats. Now, center the needle on the piece of cork. It will turn towards the north very slowly. This is the easiest way to make a magnetic compass.

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