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
                                                          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
  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.