In a double-slit experiment,the distance between the slits is $d$. The screen is at a distance $D$ from the slits. If a bright fringe is formed opposite to one of the slits,its order $n$ is:

In $YDSE$ experiment,when two light rays form the third minima,they have:

In a Young's double-slit experiment,the distance between the two slits is $d = \lambda / 4$,where $\lambda$ is the wavelength of the light used. The initial phase difference is $\pi / 4$. What is the intensity at $\theta = 30^o$?

Assertion : No interference pattern is detected when two coherent sources are infinitely close to each other.
Reason : The fringe width is inversely proportional to the distance between the two slits.

$A$ Young's double slit experiment apparatus has slits separated by $0.2 \ mm$ and a screen $60 \ cm$ away from the slits. The whole apparatus is immersed in a liquid medium of refractive index $\mu = \frac{11}{9}$ and the slits are illuminated with green light $(\lambda = 550 \ nm$ in vacuum$)$. Find the fringe width of the pattern formed on the screen. (in $mm$)

In $Y.D.S.E.$,the separation between the two slits $S_1$ and $S_2$ is $a$,and the screen is at a distance $x$ from the slits. The light source $S$ is moving with velocity $v$ parallel to the line joining $S_1$ and $S_2$ and is at a perpendicular distance $h$ from the plane of the slits. What is the frequency of change in brightness at the central point on the screen?