Thus, all
incident rays of angles in the range 0 < i < 60° will suffer total
internal reflections in the pipe (If the length of the pipe is
finite, which it is in practice, there will be a lower limit on i
determined by the ratio of the diameter to the length of the
pipe )
(b)
If there is no outer coating, i¢c = sin–1(1/1 68) = 36