Page 142 - How It Works - Book of Amazing Answers To Curious Questions, 12

� AMAZIG ANSWERS TO CURIOUS QUESTIONS -------------------

How do cigarette
filters work?

ilters were added to cigarettes in the
FFifties when it was discovered that
smoking causes lung cancer, leaving cigarette
manufacturers under pressure to convince
people that smoking was safe. The filters are
made of a synthetic fibrous mass called
cellulose acetate, which is a kind of fine plastic
packed tightly so that it looks like cotton wool.
The material is designed to accumulate the
vapours and tar in the fibres before they reach
the smoker's mouth. However, filters in no way
lessen the unhealthy smoke being inhaled. In How do fibre optics transfer data?
fact, chemicals are added to make cigarettes
taste better and to increase the speed at ibre optics represents an evolutionary leap Cladding has a lower refractive index than the
which nicotine is delivered to the brain, F in the speed and bandwidth capacity of core, causing a phenomenon called total
thereby keeping users hooked. telecommunications systems. Copper cable, internal reflection. When light strikes the
once the standard for phone lines, can transmit cladding at a low enough angle, it is reflected
�<=a
a few million electrical signals per second, back into the core without losing any energy.
while fibre can handle 20 billion light pulses per There are two major types of fibre optic
second. To understand how fibre optic cables cables: single-mode and multi-mode. Single
work, think of them as long tubes with mirrored mode fibre has the narrowest core - a tenth of
walls. If you were to shine a laser pointer into the diameter of a human hair - and uses a
the tube at a slight angle, the laser beam would powerful laser to send data long distances.
bounce its way down the tube, reflecting off Multi·mode fibre has a wider core with room to
the mirrored walls until it reached the end. bounce around many simultaneous signals.
Instead of using mirrors, the walls of fibre Multi-mode fibre uses weaker (and much less
How do lenses optic cable are made of two concentric layers expensive) LED lights and is better suited for
of silica glass called the core and cladding.
short runs like local computer networks.
magnify or '' Copper cable can transmit a few million

minimise things? electrical signals per second, while fzbre can

J\ lens is a transparent piece of glass or handle 20 billion light pulses per second ''
..l"lastic with at least one curved surface.
Light moves faster in air than it does through
glass or plastic. So, when a beam hits a lens, it
slows down. And when a beam enters glass at
an angle, the part of the beam that hits the
glass first slows down sooner making the
beam turn. Once the beam hits the air again, it
speeds up and completes the trajectory. In this
way, a lens can focus the light from an object
into an image of the object on the other side.
Convex lenses (sometimes called positive
lenses) which are thick in the middle and
curve out on one or both sides, take the light
beams and redirect them towards the
centre. Convex lenses are also called
converging lenses. Concave, or diverging
lenses, are thick at the edges and curve
inward on one or both sides. Concave
lenses take light beams and redirect
them away from the centre. Concave
lenses are used in things like TV
projectors to make light rays spread
out into the distance.

142 How It TM!rks WorldMags.net
WorldMags.net