Question

What is the required condition, if the light incident on one face, does not emerge from the other face ?

Answer 1

For no emergence for all rays incident at prism,
we can say that if r2(min) is able to do total internal reflection than definetely all value of r2 will perfom Total Internal Reflection because min r2 has performed that, so for min r2, r1 has to be maximum hence i will be maximum. Applying snell's law we'll get sinr1=1/u =critical angle
And for no emergence r2 min will be consider as greater than critical angle and hence rest r2 will be automatically eligible for Total IRnternal Reflection.
From relation r1+r2=A
We will get r1 + r2 > 2critical angle
A >2 critical angle
And this is the condition for no emergence of light.