Propagation of Light


 
 
Concept Explanation
 

Propagation of Light

Light travels along straight lines in a medium or in vacuum. The path of light changes only when there is an object in its path or where the medium changes. We call this rectilinear (straight-line) propagation of light. Light that starts from a point A and passes through another point B in the same medium actually passes through all the points on the straight-line AB. Such a straight-line path of light is called a ray of light.

Light rays start from each point of a source and travel along straight lines till they fall on an object or a surface separating two media (mediums). A bundle of light rays is called a beam of light.

Three main processes generally occur when light passes between boundaries from one medium to another.

  • Transmission: happens when light get absorbed by the medium like glass and  does not get reflected, absorbed and scattered.
  • Reflection: The process through which light rays falling on a smooth  surface are sent back. It help us to see things around us.
  • Refraction: It is the change in the direction of wave passing from one medium to other.
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    Sample Questions
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    Question : 1

    Which of the following are correct ?

    (a) Light travels along straight lines in a medium or in vacuum.

    (b) The refraction is the change in the direction of wave passing from one medium to other.

    (c) A medium in which light cannot travel is called opaque. Wood, metals, bricks, etc .

    Right Option : D
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    Explanation
    Question : 2

    A medium in which light can travel freely over large distances is called a transparent medium. Water, glycerin, glass and clear plastics are _____________________ .

    Right Option : A
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    Explanation
    Question : 3

    Statement (i) : Light travels in a straight line.

    Statement (ii) : Light requires a medium to travel.

    Right Option : A
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    Explanation
     
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