HISTORY OF MAGNET: Magnetism has been known to human being for many thousands of years. Lodestone, a magnetized form of the iron oxide mineral magnetite which has the property of attracting iron objects, is referred to in old European and Asian historical records, around 800 BC in Europe and earlier in the East, around 2600 BC. The root of the English word magnet is the Greek word magnes, thought to be derived from Magnesia in Asia Minor, once an important source of lodestone. Lodestone was used as a navigational compass as it was found to orient itself in a north-south direction if left free to rotate by suspension on a string or on a float in water.
THE COMPASS
A compass is an instrument which is used to find the direction of a magnetic field. A compass consists of a small metal needle which is magnetised itself and which is free to turn in any direction. Therefore, when in the presence of a magnetic field, the needle is able to line up in the same direction as the field.
Compasses are mainly used in navigation to find direction on the earth. This works because the earth itself has a magnetic field which is similar to that of a bar magnet (see the picture below).
The compass needle aligns with the magnetic field direction and points north (or south). Once you know where north is, you can figure out any other direction. A compass can be used in conjunction with a clock and a sextant to provide a very accurate navigation capability. This device greatly improved maritime trade by making travel safer and more efficient.
Any instrument with a magnetised pointer or needle turning freely upon a pivot and pointing in a northerly and southerly direction can be considered a compass. A picture of a compass is shown in right hand side.
Some animals can detect magnetic fields, which helps them orientate themselves and find direction. Animals which can do this include pigeons, bees, Monarch butterflies, sea turtles and fish.
MAGNET POLES
In 1269, Frenchmen Peter Peregrinus and Pierre de Maricourt, using a compass and a lodestone, found that the magnetic force of the lodestone was different at the opposite ends, which they defined to be the poles of the magnet.
MAGNETIC ATTRACTION AND REPULSION: Opposite poles of a magnet attract each other and bringing them together causes their magnetic field lines to converge (come together). Like poles of a magnet repel each other and bringing them together causes their magnetic field lines to diverge (bend out from each other). This means that two N poles or two S poles will push away from each other while a N pole and a S pole will be drawn towards each other.
Like poles of magnets repel one another while unlike poles attract. These poles always occur in pairs. It is impossible to isolate a single pole. Breaking a piece of magnet in half results in two pieces, each with it's own pair of poles.
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