Question

When light is incident on a soap film of thickness $5\times {10}^{-5}cm$, the wavelength of light reflected maximum in the visible region is $5320\stackrel{o}{A}$. Refractive index of the film will be ?

• A. 1.22
• B. 1.51
• C. 1.83
• D. 1.33

Answer 1

The correct option is D

1.33

Explanation for correct answer:

1. When the light reflected is maximum, it is the condition of constructive interference.
2. The condition for constructive interference is, $\mu =\frac{(2n+1)\lambda }{4t}$ where $n$is the principal quantum number, $\lambda$ is the wavelength of light used and $t$ is the thickness of the film.
3. Since the incident light is in visible region, $n=2$. Substituting all the given data in the above equation, $$\begin{gathered} \mu =\frac{5\times 5320\times {10}^{-10}}{4\times 5\times {10}^{-7}} \\ \mu =1.33 \end{gathered}$$

Hence, option D is the correct answer.