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,

The direction of the second maximum in the Fraunhofer diffraction pattern at a single slit is given by ($a$ is the width of the slit),