(i) Refractive index of a medium is the ratio of speed of light (c) in the free space to the speed of light (v) in that medium.
\(μ=\frac{c}{v}\)
(ii) \(μ=\frac{c}{v}=\frac{1}{sin\,i_c}\)
\(\frac{3 \times 10^8}{v}=\frac{1}{\frac {30}{50}}\)
\(v=\frac{30}{50}\times3\times10^8=1.8\times10^8m/s\)
