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AlexAnder GrAhAm Bell
The inventor of the telephone
was a Scottish-American
teacher named Alexander
Graham Bell (1847-1922).
In 1875, Bell was
experimenting with early
telegraph systems. For
this he used vibrating
steel strips called reeds.
He found that when a
reed at one end of the
line vibrated, a reed at
the other end gave out
a sound. In 1876, Bell
patented the world’s first
practical telephone.Find out more
Internet
Radio
Satellites
TechnologyWITH THe puSH of a few buttons on the telephone, it is possible to
talk to someone nearly anywhere else in the world. By making instant
communication possible, the telephone has done more to “shrink” the
world than almost any other invention. A telephone signal can take
several forms on its journey. Beneath the city streets it travels in the form of
electric currents in cables, or as light waves in thin glass fibers. Telephone
signals also travel as radio waves when they beam down to other countries
via satellites or when they carry messages to and from cell phones. Many
electronic devices “talk” to each other by sending signals via telephone
links. Computers exchange information and programs with one another,
and fax machines use telephone lines to send copies of pictures and text to
other fax machines across the world within seconds.TelepHone HAndSeT
A small direct (one-way) electric
current flows in the wires connected
to a telephone handset. Signals
representing sounds, such as callers’
voices and computer data, consist of
rapid variations in the strength
of this current.Telephones
TelepHone neTWoRk
Computer-controlled telephone
exchanges make the connections
needed to link two telephones.
When a person dials a telephone
number, automatic switches at
the local exchange link the
telephone lines directly.
International calls travel
along undersea cables or,
in the form of radio waves,
by way of radio towers.Communication satellites orbit
Earth at such a height and speed
that they remain stationary over the
same part of the globe all the time.
They receive telephone signals from
one country on Earth, boost the
signals, then beam them back
down to another country.Satellite beams
downs the signals
to Earth.Multiple base
stations allow many
phones to connect
at the same time.Cellphone
transmits signals
to a nearby tower.
Fiber-optic cables use
light waves to carry
thousands of phone
calls at one time.FAx
A facsimile, or fax, machine scans
a page by measuring its brightness
at thousands of individual points.
It then sends signals along the
telephone wire, each representing
the brightness at one point. A
printer inside the receiving fax
machine prints a dot wherever the
original picture is dark, making a
copy. Today, email is increasingly
replacing the fax.poRTABle pHoneS
A cordless telephone
has a built-in radio
transmitter and receiver. It
communicates with a unit
connected to a telephone
line in a home. Cell phones
(left) work with the aid of
local base stations and
cellular exchanges. Cell
phones are becoming
increasingly versatile. Many
now also function as cameras
and can connect to the Internet.US_516_Telephones.indd 516 12/02/16 11:19 am