Q 12-10-016NEETJEE MainMedium
A thin transparent sheet of refractive index $1.5$ placed over one slit of a Young's double slit arrangement shifts the central fringe by $5$ fringes. If the wavelength is $600$ nm, the thickness of the sheet is
Answer: (A) $6\ \mu$m
Concept. The sheet adds an optical path $(\mu - 1)t$; a shift of $n$ fringes needs $(\mu - 1)t = n\lambda$.
Step 1. Solve.
$$t = \frac{5 \times 600 \times 10^{-9}}{0.5} = 6 \times 10^{-6}\ \text{m} = 6\ \mu\text{m}$$
Answer. $6\ \mu$m (Option A).
Solution by Sreeraj P, M.Sc Physics