In Young's double slit experiment,if the width (aperture) of the source slit $S$ is increased while keeping other parameters constant,then the interference fringes will:

As shown in the figure,two point coherent sources $S_1$ and $S_2$ are placed at a small distance $d$ apart. The fringes formed on the screen will be .......

In Young's double slit arrangement,water is filled in the space between the screen and the slits. Then:

$A$ thin plastic sheet of refractive index $1.6$ is used to cover one of the slits of a double slit arrangement. The central point on the screen is now occupied by what would have been the $7^{th}$ bright fringe before the plastic was used. If the wavelength of light is $600 \ nm$, what is the thickness (in $\mu m$) of the plastic sheet?

Two coherent narrow slits emitting light of wavelength $\lambda$ in the same phase are placed parallel to each other at a small separation of $3 \lambda$. The light is collected on a screen $S$ which is placed at a distance $D (>> \lambda)$ from the slits. Find the smallest distance $x$ from the center $O$ such that the point $P$ is a maxima.

In the $YDSE$ shown,the two slits are covered with thin sheets having thickness $t$ and $2t$,and refractive index $2\mu$ and $\mu$ respectively. Find the position $(y)$ of the central maxima.