Download Theme 2: The story of Magnets

Open Text Material
Class VI
Subject - Science
Theme 2: The story of Magnets
The most popular legend accounting for the discovery of magnets is that of an elderly Cretan
shepherd named Magnes. Legend has it that Magnes was herding his sheep in an area of
Northern Greece called Magnesia, about 4,000 years ago. Suddenly both, the nails in his shoes
and the metal tip of his staff became firmly stuck to the large, black rock on which he was
standing. To find the source of attraction he dug up the Earth to find lodestones (load = lead or
attract). Lodestones contain magnetite, a natural magnetic material (Fe3O4). This type of rock
was subsequently named magnetite, after either Magnesia or Magnes himself. William Gilbert in
1600 first realized that the Earth was a giant magnet and that magnets could be made by beating
wrought iron. He also discovered that heating resulted in the loss of induced magnetism.
A magnet is any object that has a magnetic field. It attracts ferrous objects like pieces of iron,
steel, nickel and cobalt. In the early days, the Greeks observed that the naturally occurring
'lodestone' attracted iron pieces. From that day onwards began the journey into the discovery of
magnets.
These days magnets are made artificially in various shapes and sizes depending on their use. One
of the most common magnets - the bar magnet - is a long, rectangular bar of uniform crosssection that attracts pieces of ferrous objects. The magnetic compass needle is also commonly
used. The compass needle is a tiny magnet which is free to move horizontally on a pivot. One
end of the compass needle points in the North direction and the other end points in the South
direction. The end of a freely pivoted magnet will always point in the North-South direction.
The end that points in the North is called the North Pole of the magnet and the end that points
South is called the South Pole of the magnet. It has been proven by experiments that like
magnetic poles repel each other whereas unlike poles attract each other.
Remember the force when you held two magnets close and felt them either attract (pull toward
one another) or repel (push away)? One of the most amazing things about magnets is the way
they can attract other magnets (or other magnetic materials) "at a distance," invisibly, through
what we call a magnetic field.
You might be surprised just how many things around you work by magnetism or
electromagnetism. Every electric appliance with an electric motor in it (everything from your
electric toothbrush to your lawn mower) uses magnets to turn electricity into motion. Motors use
electricity to generate temporary magnetism in wire coils. The magnetic field thus produced
pushes against the fixed field of a permanent magnet, spinning the inside part of the motor
around at high speed. You can harness this spinning motion to drive all kinds of machines.
There are magnets in your refrigerator holding the door closed. Magnets read and write data
(digital information) on your computer's hard drive and on cassette tapes in old-fashioned
personal stereos. More magnets in your hi-fi loudspeakers or headphones help to turn stored
music back into sounds you can hear. If you're sick with a serious internal illness, you might
have a type of body scan called NMR (nuclear magnetic resonance), which draws the world
beneath your skin using patterns of magnetic fields. Magnets are used to recycle your metal
trash. Steel food cans are strongly magnetic but aluminum drinks cans are not, so a magnet is
used to separate the two different metals.
Que.1) How was magnet first discovered? How was the first “man-made” magnet made? (3+2)
Que.2) What are the properties of a magnet? Write the uses of magnets.
(3+2)