$A$ light of wavelength $5890 \; \mathring{A}$ falls normally on a thin air film. What is the minimum thickness of the film such that the film appears dark in reflected light?

$A$ parallel beam of light of intensity $I_0$ is incident on a coated glass plate. If $25 \%$ of the incident light is reflected from the upper surface and $50 \%$ of the light that enters the glass is reflected from the lower surface of the glass plate,the ratio of maximum to minimum intensity in the interference region of the reflected light is

$A$ soap film with refractive index $\mu = 4/3$ is illuminated by white light incident at an angle of $60^\circ$. $A$ dark band corresponding to a wavelength of $5500 \, \mathring{A}$ is observed in the reflected light. Find the minimum thickness of the film in $\mathring{A}$.

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

An oil film flowing on water appears coloured due to interference. For observing this effect,the approximate thickness of the oil film should be:

White light may be considered to be a mixture of waves with $\lambda$ ranging between $3900\ \mathring A$ and $7800\ \mathring A$. An oil film of thickness $10,000\ \mathring A$ is examined normally by reflected light. If $\mu = 1.4$,then the film appears bright for