Optics Question 118
Question: Two transparent slabs have the same thickness as shown. One is made of material A of refractive index 1.5. The other is made of two materials B and C with thickness in the ratio 1 : 2. The refractive index of C is 1.6. If a monochromatic parallel beam passing through the slabs has the same number of waves inside both, the refractive index of B is
Options:
A) 1.1
B) 1.2
C) 1.3
D) 1.4
Show Answer
Answer:
Correct Answer: C
Solution:
For A Total number of waves = $ \frac{(1.5)t}{\lambda } $ ….(i)
$ \because \begin{aligned} \text{Total number} \ \text{ of waves} \ \end{aligned} = \left( \frac{\text{optical path length}}{\text{wavelength}} \right)$
For B and C Total number of waves = $ \frac{n _{B}( \frac{t}{3} )}{\lambda }+\frac{(1.6)( \frac{2t}{3} )}{\lambda } $ ….(ii) Equating (i) and (ii) $ n _{B}=1.3 $
