Question

Considering normal incidence of ray, the equivalent refractive index of combination of two slabs shown in figure is:

• A. 1.8
• B. 1.43
• C. 2
• D. none of these

Answer 1

Answer: (B)

1.43

Answer 2

The equivalent refractive index of combination of slabs for normal incidence is $\mu=\frac{\Sigma t_{i}}{\Sigma \frac{t_{i}}{\mu_{i}}}$ In this case, $\mu=\frac{t_{1}+t_{2}}{\frac{t_{1}}{\mu_{1}}+\frac{t_{2}}{\mu_{2}}}$ $=\frac{10+15}{\frac{10}{4 / 3}+\frac{15}{3 / 2}}$ $=\frac{25}{7.5+10}=\frac{25}{17.5}$ $=1.43$