It is necessary to coat a glass lens with a non-reflecting layer. If the wavelength of the light in the coating is $\lambda$,the best choice is a layer of material having an index of refraction between those of glass and air and a thickness of

In a Fresnel biprism experiment,the eyepiece is placed at a distance of $120 \, cm$ from the source. The distance between the two virtual images is found to be $0.075 \, cm$. If the eyepiece is moved by $1.92 \, cm$ to cross $20$ fringes in the field of view,what is the wavelength of light in $\mathop A\limits^o$?

In a biprism experiment,monochromatic light of wavelength $\lambda$ is used. The distance between the two coherent sources $d$ is kept constant. If the distance between the slit and the eyepiece $D$ is varied as $D_1, D_2, D_3, D_4$ and the corresponding measured fringe widths are $W_1, W_2, W_3, W_4$,then:

$A$ thin film of soap solution $(n = 1.4)$ lies on the top of a glass plate $(n = 1.5)$. When visible light is incident almost normal to the plate,two adjacent reflection maxima are observed at two wavelengths $420 \ nm$ and $630 \ nm$. The minimum thickness of the soap solution is.....$nm$

On a rainy day,a small oil film on water shows brilliant colours. This is due to:

$A$ plano-convex lens is placed with its curved surface on a plane glass plate,creating a thin air film. With monochromatic light,this thin film produces an interference pattern due to reflections from the top curved surface and the bottom glass plate surface.
Statement-$1$: When light is reflected from the air-glass plate interface,it undergoes a phase change of $\pi$.
Statement-$2$: The center of the interference pattern is dark.