CBSE Class 12-science Answered

when light goes from denser medium to the rarer medium obliquely then some  part of it reflected and some part of it refracted, now if we keep on increasing the value of incidence angle the value of refracting angle also increasese. since refracting part is in the rarer medium so it increases with the larger value than that of angle of incidence, in for certain value of  "i"  then angle of refraction becomes 90 degrees, this value of i  is called  crictical angle of incidence, now if we increase the v alue of incidence angle  more than the critical value the value of angle of refraction goes more than ninty degrees, that is all the rays of light come back to the denser medium again, this phenonmenon is called total internal reflection of light.