Page 137 - Science Class 07
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             Light









               •  Sources of Light             •  Brightness of Light         •  Luminous Bodies
               •  How Does Light Travel?       •  Speed of Light              •  Reflec on of Light
               •  Reflec on Terms               •  Two Laws of Reflec on        •  Plane Mirror
               •  Uses of Plane Mirrors        • Kinds of Reflec on            •  Kaleidoscope             •  Periscope

               • Spherical Mirrors             •  Image By Convex Mirror  •  Image by Concave Mirror
               •  Uses of Concave Mirrors      •  Uses of Convex Mirrors      •  Light and  the Living Beings

              You  will  be  surprised  to  know  that  people  in   When the light strikes on any object, it bounces
              the  past  believed  that  light  was  there  in  the   off in all direc ons. This is called sca ering of
              eyes of the beholders (creatures). According to       light.
              them, it shot from the eyes to the seen object                       SOURCES OF LIGHT
              and then returned to the eyes with an image of
                                                                    An object that emit light from its own body is
              that object. It was during the 16th century that
                                                                    called a source of light. Sources of light fall into
              discoveries were made regarding light. It came
                                                                    two groups– natural and ar ficial.
              to  be  proved  that  light  is  a  form  of  energy
              which can travel freely in straight lines through     Natural sources of light include the sun, stars,
              its rays.                                             fire  flies  and  animals  that  give  out  light  from
                                                                    their bodies.
              The  light  energy  is  a  radiant  energy  that
              contains  radio-waves,  X-rays,  ultraviolet  rays    Ar ficial  sources  of  light  are  electric  lights,
              and  infrared  rays,  but  all  these  rays  are  not   candles, oil-lamps, camps-fires, torches, lasers,
              visible to the eye. The part of the light that we     etc.

              see is called visible light.                          When  the  light  coming  from  a  source  falls  on
              Remember  that,  all  light  comes  from  atoms       an  object,  it  sca er  around  and  brightens  the
              when  they  gain  extra  energy  either  from         object. Some of this sca ering light reaches the
              another  source  or  on  ge ng    excited  when       eyes of the beholder and he or she is able to

              struck  by  other  par cles.  This  extra  energy     see  that  object.  Moreover,  some  of  this  light
              begins to emit light.                                 sca ers  to  nearby  shady  areas,  i.e.,  the  areas

              Science-7                                                                                         137
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