Q 12-10-145JEE MainJEE Main 2019 (12 Apr, Shift 1)Easy
In a double slit experiment, when a thin film of thickness $t$ having refractive index $\mu$ is introduced in front of one of the slits, the maximum at the centre of the fringe pattern shifts by one fringe width. The value of $t$ is ($\lambda$ is the wavelength of the light used):
Answer: (D) $\dfrac{\lambda}{\mu - 1}$
The film adds an optical path $(\mu - 1)t$. A shift of one fringe needs one wavelength:
$$(\mu - 1)t = \lambda \Rightarrow t = \frac{\lambda}{\mu - 1}$$
Solution by Sreeraj P, M.Sc Physics