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 a denser medium to a rarer medium. When Swarali increased the values of the angle of incidence (i ), the values of the angle of refraction (r ) went on increasing. But at a certain angle of incidence, the light rays returned into the denser medium.
So, Swarali has some question. 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 the denser medium. Explain the process.

Explanation

(a) Critical angle
`r = 90^(@)`
(b) Total internal reflection.
As light goes from a denser to rarer medium, if the value of the angle of incidence increases, then the value of the angle of refraction also increases. But after a specific angle of incidence called the critical angle, the light gets reflected back into the denser medium.