A thin plastic sheet of refractive index $1.6$ is used to cover one of the slits of a double-slit arrangement. The central point on the screen is now occupied by what would have been the $7$ bright fringe before the plastic was used. If the wavelength of light is $600 \mathrm{nm}$, what is the thickness (in $\mu \mathrm{m}$) of the plastic? 

In Fresnel's experiment, the width of the fringe depends upon the distance 

Fringes are produced with monochromatic light of wavelength $5.45\times {10}^{-5} \mathrm{cm}$. A thin glass plate of R.I. $1.5$ is then normally placed in one of the paths of interfering waves and the central bright band of the fringe system is found to move into the position, previously occupied by the third bright band from the system. The thickness of the glass plate will be 

Biprism experiment is conducted with a wavelength of $5000 \stackrel{0}{\mathrm{A}}$. The distance between the virtual sources is $0.2 \mathrm{mm}$ and the micrometer eyepiece is at a distance of $100 \mathrm{cm}$ from the slits. The distance between the consecutive bright and dark band is

The distance of a point on the screen from two slits in biprism experiment is $1.8\times {10}^{-5} \mathrm{m}$ and $1.23\times {10}^{-5} \mathrm{m}$. If wavelength of light used is $6000 \stackrel{0}{\mathrm{A}}$, the fringe formed at that point is 

To observe diffraction, the size of the obstacle 

The $X-$rays can not be diffracted by means of an ordinary grating because of 

In a Fraunhofer diffraction at a single slit, if yellow light illuminating the slit is replaced by blue light, then diffraction bands 

For Fraunhofer diffraction to occur