When white light is incident normally on an oil film of thickness $10^{-4} \,cm$ and refractive index $1.4$,the wavelength which will not be seen in the reflected system of light is ........... $\mathring{A}$.

The colours observed in thin soap bubbles are due to

In a biprism experiment,a wavelength $\lambda$ is used to obtain an interference pattern. The fringe width is $W_1$ at a distance $D_1$ from the screen. When the screen is moved towards the biprism,the fringe width becomes $W_2$ at a distance $D_2$. The distance between the two virtual images of the slit is:

When petrol leaking from a vehicle falls on a rain-wet road,colours are observed. This is due to the.......... of light.

In a biprism experiment,a steady interference pattern is observed on the screen using light of wavelength $\lambda_1 = 5000 \ Å$. Without disturbing the setup of the experiment,the source of light is replaced by a source of wavelength $\lambda_2 = 6400 \ Å$. The fringe width will:

The beautiful iridescent (like a rainbow) colors on the wings of a tropical or morpho butterfly are due to