• # question_answer 52) A glass slab has the left half of refractive index ${{n}_{1}},$ and the right half of${{n}_{2}}=3{{n}_{1}}$. The effective refractive index of the whole slab is A)  $\frac{{{n}_{1}}}{2}$                       B)  $2n$C)  $\frac{3{{n}_{1}}}{2}$                             D)  $\frac{2{{n}_{1}}}{2}$

Total time taken to travel distance d is : $\frac{d}{2{{n}_{1}}}+\frac{d}{2{{n}_{2}}}=d\left( \frac{{{n}_{1}}+{{n}_{2}}}{2{{n}_{1}}{{n}_{2}}} \right)=\frac{d}{{{n}_{eff}}};$${{n}_{2}}=3{{n}_{1}}\Rightarrow {{n}_{eff}}=\frac{3}{2}{{n}_{1}}$