If${}_{\mathit{a}}^{}{\mathit{\mu }}_{\mathit{m}}^{}$ is the refractive index of the denser medium with respect to the rarer medium and ' $\mathit{c}$ ' is the critical angle for the pair of media then the relation between them is
${}_{\mathit{d}}{\mathit{\mu }}_{\mathit{m}}=\frac{1}{\mathit{s}\mathit{i}\mathit{n}\mathit{C}}=\mathrm{cosec}\mathit{C}$