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Class 10
Chapter 11 Class 10 - Human Eye and Colourful World

Assertion (A): In case of a rainbow, light at the inner surface of the water drop gets internally reflected.  

Reason (R): The angle between the refracted ray  and normal to the drop surface is greater than the  critical angle.  


Let’s look at how a rainbow is formed

  • After rain , there are many tiny droplets of water still in the air
  • When sunlight falls on these droplets
  • These droplets act as tiny prisms
  • When sun rays fall on these droplets, the rays get first refracted , then internally reflected and then refracted again
  • Due to this different colors of sunlight are bent at different angles and we are able to see a spectrum in the form of a rainbow

How is rainbow formed-01.jpg


Since light at the inner surface gets internally reflected, Assertion is true

For critical angle,

  • Total internal reflection only takes place if the light from a denser medium to a lighter medium strikes at an angle of incidence larger than the critical angle
  • If the angle between the refracted light and the normal to the drop surface is greater than a critical angle ( which is 45 degrees), the light reflects off the back of the drop .
  • If the angle between the refracted light and the normal to the drop surface is less than the critical angle , the light will simply pass through .

Critical Angle in Refraction.jpg

Therefore, r easoning is also a true and correct explanation of assertion .  



  • Assertion is True
  • Reason is True
  • And reason is the correct explanation for the assertion.

So, the correct answer is (a) 

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CA Maninder Singh is a Chartered Accountant for the past 13 years and a teacher from the past 17 years. He teaches Science, Economics, Accounting and English at Teachoo