NO.215 Which of the following cables is made of glass or plastic and transmits signals in the form of light?
Fiber optic cable is also known as optical fiber. It is made of glass or plastic and transmits signals in the form of
light. It is of cylindrical shape and consists of three concentric sections: the core, the cladding, and the jacket.
Optical fiber carries much more information than conventional copper wire and is in general not subject to
electromagnetic interference and the need to retransmit signals. Most telephone company’s long-distance lines
are now made of optical fiber. Transmission over an optical fiber cable requires repeaters at distance intervals.
The glass fiber requires more protection within an outer cable than copper.
Answer option B is incorrect. Twisted pair cabling is a type of wiring in which two conductors (the forward and
return conductors of a single circuit) are twisted together for the purposes of canceling out electromagnetic
interference (EMI) from external sources. It consists of the following twisted pair cables:
Shielded Twisted Pair: Shielded Twisted Pair (STP) is a special kind of copper telephone wiring used in some
business installations. An outer covering or shield is added to the ordinary twisted pair telephone wires; the
shield functions as a ground. Twisted pair is the ordinary copper wire that connects home and many business
computers to the telephone company. Shielded twisted pair is often used in business installations. Unshielded
Twisted Pair: Unshielded Twisted Pair (UTP) is the ordinary wire used in home. UTP cable is also the most
common cable used in computer networking. Ethernet, the most common data networking standard, utilizes
UTP cables. Twisted pair cabling is often used in data networks for short and medium length connections
because of its relatively lower costs compared to optical fiber and coaxial cable.UTP is also finding increasing
use in video applications, primarily in security cameras. Many middle to high-end cameras include a UTP
output with setscrew terminals. This is made possible by the fact that UTP cable bandwidth has improved to
match the baseband of television signals.
Answer option A is incorrect. Coaxial cable is the kind of copper cable used by cable TV companies between
the community antenna and user homes and businesses. Coaxial cable is sometimes used by telephone
companies from their central office to the telephone poles near users. It is also widely installed for use in
business and corporation Ethernet and other types of local area network. Coaxial cable is called “coaxial”
because it includes one physical channel that carries the signal surrounded (after a layer of insulation) by
another concentric physical channel, both running along the same axis. The outer channel serves as a ground.
Many of these cables or pairs of coaxial tubes can be placed in a single outer sheathing and, with repeaters,
can carry information for a great distance. It is shown in the figure below:
Answer option C is incorrect. Plenum cable is cable that is laid in the plenum spaces of buildings. The plenum
is the space that can facilitate air circulation for heating and air conditioning systems, by providing pathways for
either heated/conditioned or return airflows. Space between the structural ceiling and the dropped ceiling or
under a raised floor is typically considered plenum. However, some drop ceiling designs create a tight seal that
does not allow for airflow and therefore may not be considered a plenum air-handling space. The plenum
space is typically used to house the communication cables for the building’s computer and telephone network.
