```Scattering of Light                                  Convex or Convergent Lens
  When light passes through a substance or
gas, a part of it is absorbed and the rest
scattered away.
  The strength of scattering can be measured
by the loss of energy in the light beam as it
passes through the medium.
  A clear cloudless day-time sky is blue                It is a positive lens.
because molecules in the air scatter blue             Convex lenses are thicker at the middle.
light from the sun more than they scatter              Rays of light that pass through the lens are
red light.                                             brought closer together (they converge).
  When we look towards the sun at sunset,               When parallel rays of light pass through a
we see red and orange colours because the              convex lens the refracted rays converge at
blue light has been scattered out and away             one point called the principal focus.
from the line of sight.                               The distance between the principal focus
  When sunlight is intercepted by a drop of              and the center of the lens is called the
water in the atmosphere, some of the light             focal length.
refracts into the drop, reflects from the
Concave or Divergent lens
drop"s inner surface, and then refracts out
of the drop. The first refraction separates
the sunlight into its component colours,
and the second refraction increases the
separation. The result is a rainbow.
Optical Fiber
  It is a thin glass fibre through which light          It is a negative lens.
can be transmitted.                                   Convex lenses are thinner at the middle.
  A fiber optic cable consists of a bundle of            Rays of light that pass through the lens are
glass threads, each of which is capable of             spread out (they diverge).
transmitting messages modulated onto                  When parallel rays of light pass through a
light waves. It can function as a                      concave lens the refracted rays diverge so
waveguide, or “light pipe”, to transmit                that they appear to come from one point
light between the two ends of the fiber.               called the principal focus.
    The distance between the principal focus
Lens
and the center of the lens is called the
  It is an optical device which transmits and            focal length.
refracts light, converging or diverging the           The image formed is virtual and
beam.                                                  diminished (smaller).
  A simple lens consists of a single optical
Focal Point
element.
  A compound lens is an array of simple             It is generally noted by the capital letter "F."
lenses with a common axis.                        This is the point in space where the light rays
  Lenses are two types: Convex and                  will converge to after passing through a
Concave                                           converging lens.
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