Light

LIGHT

  • Light is a form of energy, (optical energy) which helps us in seeing objects by its presence.
  • Light travels in a straight line with 3 × 108 m/s in vaccum..
  • The velocity of light changes when it travels from one medium to another.
  • Light gets reflected back from polished surfaces, such as mirrors, polished metal surfaces, etc.
  • Light undergoes refraction (bending) when it travels from one transparent medium to another.

 

SOURCES OF LIGHT 

  • The objects which emit (give) light are called luminous objects. It may be natural or man-made. Sun is a natural source of light and electric lamp, and oil lamp, etc. are man-made source of light.
  • The Non-luminous objects do not emit light. However, such objects become visible due to the reflection of the light falling on them. Moon does not emit light. It becomes visible due to the reflection of the sunlight falling on it.

 

LINEAR PROPAGATION OF LIGHT

    Light travels in a straight line. In vaccum or air, light travels with the velocity of 3 × 108 m/s.
    Activity : If we see at a lighted candle through a straight pipe as shown in figure(a), we are able to see the candle but if we see the candle through a bent pipe we are not able to see the candle flame as shown in figure (b).
    This activity showed that light travels along straight lines.


                              

 

BEHAVIOUR OF LIGHT

       When light travelling in one medium falls on the surface of a second medium, the following three effects may occur.
(i)     A part of the incident light is turned back into the first medium. This phenomenon is called reflection of light. 
(ii)    A part of the incident light is transmitted into the second medium along a changed direction. This phenomenon is called refraction of light.
(iii)   The remaining third part of light energy is absorbed by the second medium. This phenomenon is called absorption of light.    

 

REFLECTION OF LIGHT

    When light rays are incident on an opaque  polished surface (medium), these are returned back in the same medium.
    This phenomenon of returning of ray of light in the same medium, is called reflection of light.

1.  Types of mirror


                        

2.  Some Associated Terms

  • Reflecting surface : The surface from which the light is reflected, is called the reflecting surface. In diagram, XY is the reflecting surface
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