The correct curve between fringe width $\beta$ and the distance between the slits $(d)$ is:

$A$ beam of light consisting of two wavelengths, $650\; nm$ and $520\; nm$, is used to obtain interference fringes in a Young's double-slit experiment.
$(a)$ Find the distance of the third bright fringe on the screen from the central maximum for wavelength $650\; nm$.
$(b)$ What is the least distance from the central maximum where the bright fringes due to both the wavelengths coincide?

In a two-slit experiment with monochromatic light,fringes are obtained on a screen placed at some distance from the slits. If the screen is moved by $5 \times 10^{-2} \ m$ towards the slits,the change in fringe width is $3 \times 10^{-5} \ m$. If the separation between the slits is $10^{-3} \ m$,the wavelength of light used is ....... $\mathring{A}$.

In a $YDSE$,if the slits are of unequal width:

Young's double-slit experiment is performed in air and then performed in water. How does the fringe width change?

In a Young's double slit experiment,the source illuminating the slits is changed from blue to violet. The width of the fringes