in France owed duties to large landowners
until the French Revolution,
which started in 1789. In Russia the
serfs did not gain freedom until 1861.
#More to explore
Knight • Middle Ages
Fiber Optics
Fiber optics is a way of sending information
through thin fibers, or threads. The
information may be sound, pictures, or
A painting shows serfs giving animals to
their lord.
14 Fiber Optics BRITANNICA STUDENT ENCYCLOPEDIA
computer codes. This information travels
through the fibers in the form of
light.
The fibers, known as optical fibers, can
be made of glass or plastic. They are
about as big around as a human hair.
Many fibers are bundled together to
form a fiber-optic cable. Fiber-optic
cables link some telephones and computers.
Doctors also use fiber-optic
instruments to see inside the human
body.
In a fiber-optic system, a machine
called a transmitter turns information
into light. Then the transmitter sends
the light through optical fibers. The
inner part of each fiber is called the
core. A reflective material surrounds the
core. This material is known as
cladding.
The cladding keeps the light moving
through the fiber. Light will move in a
straight line easily, but it will not turn a
corner without help. As the light moves
at a high speed through the core, it
bounces off the cladding. If the fiber has
a bend in it, the light can bounce off the
cladding and turn the corner to follow
the bend. The cladding also keeps the
light from losing its strength. The light
can travel quickly over long distances.
At the end of the fibers is a machine
called a receiver. It accepts the light. The
receiver turns the light back into sound,
pictures, or computer codes.
Most telephone cables used to be made
of copper wires. Fiber-optic cables are
better than old-fashioned copper wires
in many ways. Fiber-optic cables are
small and light. They can carry a lot of
information with little interference.
Fiber-optic cables are also less likely to
catch fire than copper wires. However,
Optical fibers are as thin as a human hair.
They are usually bundled together.
A layer called cladding keeps light from
escaping out of the core of an optical fiber.
BRITANNICA STUDENT ENCYCLOPEDIA Fiber Optics 15
fiber-optic cables are expensive. They
also break more easily than copper wires.
#More to explore
Computer • Light • Telephone
Fibers
Fibers are long, thin strands of material
made by plants, animals, or humans.
People use fibers to make many useful
products. Some examples are brushes,
rope, paper, carpets, and textiles (cloth).
There are two types of fibers: natural
and artificial.
Natural Fibers
Natural plant fibers include rubber and
cellulose. Cellulose is the tough part of
plants and trees. Natural animal fibers
include hair or fur and silk, which caterpillars
make to build their cocoons.
Preparing Natural Fibers
Whole natural fibers may be braided, or
crossed over and under each other, to
make things. For example, people make
baskets by braiding grasses, reeds, or
twigs. However, many natural fibers are
thin or break easily. They must be made
thicker and stronger before they can be
used to make things. This is done by
combining single fibers together.
The most common way of combining
fibers is to twist several fibers into
thicker threads. People then weave or
knit the threads into cloth. People may
also form bundles of fibers into yarn,
cord, or rope. Felt and paper are made
by tangling fibers into a sheet.
Properties and Uses
A natural fiber can be wide and thick or
long and thin. It may feel smooth or
rough. Some natural fibers are easy to
bend, while others are stiff. Silk and
cotton fibers are lightweight and soft.
Cloth made from these fibers is perfect
for clothes, bed linens, and towels. On
the other hand, wool can feel rough and
itchy. Since wool is very warm, however,
it is often used to make sweaters and
blankets.
People use natural fibers that are
bumpy, rough, and scaly to make
heavier objects. For example, straw,
jute, and hemp can be woven into
mats, hats, rope, and baskets. Bristles
(short, stiff animal hairs) work well in
hair brushes.
Artificial Fibers
Artificial fibers do not grow in nature.
Scientists design them in laboratories,
and factories make them out of special
chemicals.
Bundles of vegetable fibers from ancient
Egypt are displayed in a museum.
16 Fibers BRITANNICA STUDENT ENCYCLOPEDIA
Making Artificial Fibers
A French inventor made the first artificial
fiber, called rayon, in the late 1800s.
Rayon is made from plant cellulose that
has been changed into liquid form. The
liquid cellulose is forced through tiny
holes to make long, thin fibers. Acetate
and lyocell are other artificial fibers
made from plant cellulose.
Scientists later discovered how to make
artificial fibers from liquid chemicals.
These chemicals mainly come from
petroleum (oil) and natural gas. In the
1930s scientists used these chemicals to
create nylon. Other artificial fibers made
in this way include acrylic, spandex, and
polyester.
Properties and Uses
Artificial fibers are strong and tough.
Some, especially nylon and spandex, can
be stretched like a rubber band. People
