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GRADES K-4
JUST THE FAX
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GRADES K-4
JUST THE FAX
BACKGROUND INFORMATION:
Fax is short for facsimile, which means a copy or reproduction. A fax machine uses a sensor to "read" the black and white sections of a document. The sensor switches a signal on or off according to whether a light beam is reflected by white sections or absorbed by black sections. This information is then sent over wires or cables to the receiving machine. The receiving machine decodes the signals and marks the sections that are black.
A Scottish physicist, Alexander Bain, developed the first basic fax machine in 1842. Other facsimile machines were developed in Europe and the United States in the late 1800's and early 1900's. By the 1930's news services began using fax machines to send photographs. As the equipment became less expensive to manufacturer, the fax machine became a common office tool for businesses.
This is how a fax machine works. In the diagram you see two fax machines side-by-side. To send a fax, both parties must have a fax machine connected to a telephone line or cable. In this example, the gray fax machine (on the left) will send the fax and the white fax machine (on the right) will receive the fax.
A page is placed into the document feeder of the gray fax machine. The telephone number of the receiving white fax machine is dialed. When the telephone connection is made between the two fax machines, the document moves through the gray fax machine. The text or image on the document passes by a light sensor. The light sensor (a light sensitive device) scans the document and creates an electronic signal for the light and dark images on the document. This electronic signal is coded and sent over the telephone lines to the receiving white fax machine.
How does the white fax machine print the page? The two fax machines in this picture do not have an ink cartridge like a printer, toner like a photocopying machine or a ribbon like a typewriter. This fax machine uses a special type of paper -- "thermal" paper. The word "thermal" refers to heat. This paper is sensitive to heat. When the paper is heated, a chemical reaction occurs which creates a dark image. As the fax machine decodes the page it heats up the portion of the special paper where it wants to place letters or other markings on it.
To demonstrate this, a match was held near some thermal paper. The match did not touch the paper but the match generates heat, which warms up the paper. As you can see, the paper turns dark as it is heated. The fax machine applies heat very precisely in specific patterns so that the letters on the paper appear.
Today, many fax machines use ordinary paper instead of thermal paper. (The thermal paper is very thin and it curls, fades, and can be difficult to read and write on.) Toner similar to that used in a photocopying machine is used to make the images. Faxes can also be send to computers.
In this activity your eyes acted like the light sensor and your pencil like the toner!
References
Gale Encyclopedia of Science, (Photocopier), Vol. 5, Gale Research, New York, 1996.
The World Book Encyclopedia, (Fax Machine), World Book, Inc., Chicago, 2002.