Magnetism
A simple magnet is a magnetised bar of iron. It attracts and holds iron pieces but does not attract pieces of copper. Those materials attracted by a magnet comes under magnetic materials and those not attracted are described as non-magnetic. Examples for strong magnetic materials include iron, nickel, cobalt and certain alloys whereas copper, glass, wood, etc. are non-magnetic materials. However, in presence of strong magnets, even non-magnetic substances show feeble magnetism. A bar magnet when suspended with a thread tied exactly in its middle, after oscillating for a little it comes to rest in the north-south direction. The end pointing to north direction is called north pole of magnet and the end pointing to south direction is called south pole of magnet. Like poles of two magnets repel and unlike poles of two magnets attract.
Earth’s Magnetism
Earth also has magnetism however its origin is still not clear. It is believed that the motion of charges in the molten outer core creates the magnetic field. Earth’s magnetism may be due to heat arising from the earth’s inner core. The heat may be responsible for cause of convection currents in the molten outer core.The flow of ions and electrons would produce a magnetic field. It is probably the combination of such convection currents with the rotational effects of the earth are source of the earth’s magnetic field.The South Pole of the Earth is located upon the Antarctic Continent in the southern hemisphere.The North Pole is located in the middle of the Arctic Ocean. At any place on the earth, the magnetic north is not usually in the direction of the geographic north. The angle between the two directions is called the declination. Mariners using compasses must allow for declination in determining the true north. The angle made by a freely suspended bar magnet with the horizontal is called the dip of the place. On the equator, the dip is zero and on the poles it is 90°.
Magnetic Resonance Imaging (MRI)
MRI is a non-invasive medical test that uses a magnetic field and pulses of radio wave energy to take images of internal organs of the body.The images are examined on a computer monitor, printed or copied on a compact disc. MRI does not use x-rays.
