Which of the following phenomena produces the colour in a soap bubble?

In a biprism experiment,the fringe width is $0.6 \ mm$. The distance between the $6^{th}$ dark fringe and the $8^{th}$ bright fringe on the same side of the central bright fringe is: (in $mm$)

In a biprism experiment,the slit separation is $1 \,mm$. Using monochromatic light of wavelength $5000 \text{ Å}$,an interference pattern is obtained on the screen. Where should the screen be moved,so that the change in fringe width is $12.5 \times 10^{-5} \,m$?

If Fresnel's biprism experiment is performed in water instead of air,what will be the effect on the fringe width?

In a Fresnel's biprism experiment,coherent sources are obtained by which of the following phenomena?

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 ........... $\mathring{A}$.