\(\mu_{1} \sin \theta=\mu_{2} \sin \left(90^o-\mathrm{C}\right)\)
\(\sin \theta=\frac{\mu_{2} \sqrt{1-\frac{\mu_{1}^{2}}{\mu_{2}^{2}}}}{\mu_{1}}\)
\(\theta=\sin ^{-1} \sqrt{\frac{\mu_{1}^{2}-\mu_{2}^{2}}{\mu_{1}^{2}}}\)
For \(TIR\)
\(\theta<\sin ^{-1} \sqrt{\frac{\mathrm{u}_{2}^{2}}{\mu_{1}^{2}}-1}\)