The Science of Magnets
Magnetism is one of nature's fundamental forces. Magnetic forces are caused by the motion of charged particles such as electrons. This results in an attractive or repulsive force that acts between magnetic materials. Iron is the most common magnetic material. Magnetism has been known since ancient times. Lodestone an oxide of iron, has the property of attracting iron objects, and was known to the ancient Greeks, Romans, and Chinese. If a piece of iron is rubbed with lodestone, the iron piece acquires the ability to attract other pieces of iron. The ends of the resulting magnet are called north and south poles. Like poles repel each other and unlike poles attrach each other.
Magnets or wires carrying electric current can influence other magnetic materials
without physically contacting them. Magnetic objects produce a magnetic field. Magnetic
fields can be drawn as magnetic flux lines. At a point, the direction of the magnetic
field is the same as the direction of the flux lines, and the strength of the field is
proportional to the distance between the flux lines. In a bar magnet, the flux lines
begin on one end of the magnet, then loop around the other end. Flux lines can be imsgined
as being closed loops, with one part of the loop inside the magnet and the other part of
the loop outside the magnet.
The ends of the magnet, where the flux lines are closes has the strongest field.
The sides of the magnet, where the flux lines are far apart has a weaker magnetic
field. Different kinds of magnets produce different patterns of flux lines.
Flux lines can be mapped by using a compass or small iron filings.
Magnets tend to align themselves along magnetic flux lines. A compass, which is a small magnet
that is free to rotate, will orient itself along the earth's magnetic flux lines. If placed near a magnet
a compass will rotate to align itself with the magnet.
