Two coherent light sources, $P$ and $Q$, each of wavelength $\text{λ}$, are separated by a distance $3\text{λ}$ as shown. The maximum number of minima formed on line $AB$ which runs from $-\infty$ to $+\infty$ is,

The slits in a double-slit interference experiment are illuminated by orange light $\left(\text{λ}=600 \mathrm{nm}\right)$. A thin transparent plastic of thickness $t$ is placed in front of one of the slits. The number of fringes $\left(N\right)$ shifting on screen is plotted with the refractive index $\left(\mu \right)$ of the plastic. The value of $t$ (in $\mathrm{\mu m}$) is,

In a standard Young's double-slit setup, we get $60$ fringes on a section of screen with monochromatic light of wavelength $4000 \mathrm{Å}$. If we use monochromatic light of wavelength $6000 \mathrm{Å}$, then the number of fringes that would be obtained in the same section is,

White light is used to illuminate the two slits in a Young's double slit experiment. The separation between the slits is $b$ and the screen is at a distance $d \left(\gg b\right)$ from the slits. At a point on the screen directly in front of one of the slits, certain wavelengths are missing. One of these missing wavelengths is,