Name this certain value of ‘i ’. What is the value of ‘r’ at that time ? Name this process of returning of light in dense medium. Explain the process.

Question

Swarali has got the following observations while doing an experiment. Answer her questions with the help of observations.

Swarali observed that the light bent away from the normal, while travelling from dense medium to rarer medium. When Swarali increased the values of angle of incidence (i), the values of angle of refraction (r) went on increasing. But at a certain angle of incidence, the light rays returned into the dense medium.

So, Swarali has some questions. Answer them – 

a) Name this certain value of ‘i ’. What is the value of ‘r’ at that time ? 

b) Name this process of returning of light in dense medium. Explain the process. 

Answer 1

a) Critical angle 

 r = 90० 

 b) Internal reflection 

As light is going from denser to rarer medium, if the value of angle of incidence increases then the value of angle of reflection also increases. But after specific angle of incidence (critical angle) the light gets reflected back into the dense medium.