In Fig., find the maximum angle `i` for which light suffers total internal reflection at the vertical surface.
.

Explanation

`i_(c )+r=90^(@)`
`r=90^(@)-49.1^(@)`
`=40.9^(@)`
`sinr=sin(40.9)^(@)=0.655`
`"Also, "(sini)/(sinr)=mu=(1)/(sini_(c ))=(1)/(sin49.1^(@))`
`rArr" "sini=1.323xxsinr`
`=1.323xx0.655`
`=0.866`
`rArr" "i=sin^(-1)(0.866)~~59.9^(@)`
If the angle of incidence at vertical surface is greater than initial angle `i_(c )`, then i will be less than `59.9^(@)`. So, the maximum value of i for which the total internal reflection at BC is `59.9^(@)`.