where \(C\) is the critical angle.

Also, \(\sin C{ = ^l}{\mu _a}\)

\(\sin C = \frac{1}{{{a_{{\mu _l}}}}}\) \(\left[ {{\text{since}}{{\text{ }}^l}{\mu _a} = \frac{1}{{^a{\mu _l}}}} \right]\)

Also \(^{a} \mu_{l}=\frac{\text { velocity of light in air }(c)}{\text { velocity of light in liquid }(v)}\)

\(\therefore\)     \( \sin C=\frac{v}{c}=\frac{v}{3 \times 10^{8}}\)

or, \(\quad v=3 \times 10^{8} \times \frac{3}{5}=1.8 \times 10^{8} \,\mathrm{ms}^{-1}\)