In Young's double-slit experiment,which of the following phenomena occur?

In Young's double-slit experiment using monochromatic light,the shape of the interference pattern on the screen is .....

In the Young's double slit experiment,the distance between the slits varies in time as $d(t) = d_{0} + a_{0} \sin \omega t$; where $d_{0}$,$\omega$,and $a_{0}$ are constants. The difference between the largest fringe width and the smallest fringe width obtained over time is given as:

In a Young's double slit experiment,two slits are illuminated with light of wavelength $\lambda = 800 \, nm$. The line joining $A_1 P$ is perpendicular to $A_1 A_2$ as shown in the figure. If the first minimum is detected at $P$,the value of slit separation '$a$' will be $......... \, mm$. The distance of the screen from the slits is $D = 5 \, cm$.

In a $YDSE$ apparatus,if we use white light,then:

Assertion: $A$ white source of light during interference forms only white and black fringes.
Reason: Width of fringe is inversely proportional to the wavelength of the light used.