Question

What is total internal reflection in physics?

Answer 1

the complete reflection of a light ray reaching an interface with a less dense medium when the angle of incidence exceeds the critical angle.

Answer 2

when a ray of light travels from denser to rarer medium if the incident angle is greater than critical angle the the ray of light reflect back into medium the reverse of path of ray of light is called as total internal reflection.
if i=c then r=90°
1/u=sini/ sinr
as sinr =sin90 =1
sini =since
so
1/u =sinc
c = sin ^-1 (1/u)