In the YDSE shown, the two slits are covered with thin sheets having thickness $t$ and $2t$ and refractive index $2\mathit{\text{μ}}$ and $\mathit{\text{μ}}$, respectively. Find the position $\left(y\right)$ of the central maxima.

To make the central fringe at the centre $O$, a mica sheet of refractive index $1.5$ is introduced. Choose the correct statement.

The path difference between two interfering waves at a point on the screen is $\frac{\mathit{\text{λ}}}{6}$. The ratio of the intensity at this point and that at the central bright fringe will be (Assume that intensity due to each slit is same)

A Young's double slit experiment is conducted in water $\left({\text{μ}}_1\right)$ as shown in the figure, and a glass plate of thickness $t$ and refractive index${\text{μ}}_2$ is placed in the path of $S_2$. The magnitude of the phase difference at $O$ is (Assume that $\text{λ}$ is the wavelength of light in air,$O$ is symmetrical w.r.t.($S_1$ and $S_2$.)

In the figure shown in a Young's double slit experiment, a parallel beam of light is incident on the slits from a medium of refractive index $n_1$. The wavelength of light in this medium is ${\text{λ}}_1$. A transparent slab of thickness $t$ and refractive index $n_3$ is put in front of one slit. The medium between the screen and the plane of the slits is $n_2$. The phase difference between the light waves reaching point $O$ (symmetrical relative to the slits) is,