(a) For a ray of light travelling from a denser medium of refractive index `n_(1)` to a rarer medium of refractive index `n_(2)`, prove that `(n_(2))/(n_(1)) = sin i_(c)`, where `i_(c)` is the critical angle of incidence for the media.
(b) Explain with the help of a diagram, how the above principle is used for transmission of video signals using optical fibres.