We know magnets attract small places of iron to them and will
continue to do so, day in and day out, year after year. In short, it is a
permanent magnet, and as such has relatively little practical value.
Now by using Oersted’s discovery and the results of further
research by Faraday, a piece of iron that has no magnetic properties can instantly be turned into a magnet by winding a wire around it and
sending an electric current through the wire.
While on the face of it, this does not seem to be very
important, you can readily see that if the iron becomes a magnet when the
current flows through the coil around the iron, and ceases to be a magnet when
the current stops, motion in distant places can be caused by merely pressing a button
and closing an electric circuit.
We can, for example, pick up a needle or nail in Chicago by
pressing a button in New York if we have an electric current and a wire running
from New York to Chicago and if that wire is connected to an electromagnet in Chicago.
While it may not be
important to pick up a needle or a nail, we can rig up an electromagnet that
will pull a needle to it and produce a clicking sound by pressing and releasing
a button in New York.
This is precisely the principle of the telegraph. The telegraph
in principle is nothing more than an electromagnet over which a steel bar is
free to move up and down.
When no current flows through the coils the bar is forced up
by a spring. When current flows through the coils the iron is magnetized and it
attracts the steel bar above it, producing a distinct clicking sound. As soon
as the current stops the bar is forced back.
If the current is controlled by a key which when pressed down
produces a current and when released stops it, it follows that every time the
key is pressed down in New York a click will be heard in Chicago, and every
time it is released another click will be heard, caused by the steel bar
springing back to its original position. As you know the length of time between
clicks determines what are known as dots and dashes; a short click is a dot and
a long click is a dash.
Two systems of dots and dashes are in common use in
telegraph- the Morse code and the continental code. The electromagnet is one of
man’s most important inventions. It is used in the dynamo, the motor, the
telephone, radio, television, the talkies, the bell, block signals and modern
devices are based on the electromagnet principle. Nowadays modern people don’t know about the telegram, they know telegram messenger only.
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science