In a YDSE, a thin films of thickness$t_1 \text{and} t_2$ are placed in front of slits $S_1 \text{and} S_2$ as shown in $\text{figure-}1$ and $\text{figure-}2$. It is observed that first minima and second maxima are produced at point $O$ in first and second experiments, respectively. The points $O$ and $S$ are symmetrical with respect to $S_{1 }\text{and} S_2$. Both the films have same refractive index if $\frac{t_2}{t_1}=\frac{X}{25}$, then calculate $x$.

In Young's double slit experiment, the distance between the slits is $d$ and that between the slits and screen is $D$. The angle between principle axis of lens and perpendicular bisector of $S_1 \text{and} S_2 \text{is} 45°$. The point source $S$ is placed at the focus of lens and aperture of lens is much larger than $d$. Assuming only the reflected light from plane mirror $M$ is incident on the slits, the distance of central maxima from $O$ will be,

The figure shows a glass plate placed vertically on a horizontal table with a beam of unpolarised light falling on its surface at $57°$ with the normal. The electric vectors in the reflected light on the screen $S$ will vibrate with respect to the plane of incidence,