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

In a biprism experiment,if the $5^{\text{th}}$ bright band with wavelength $\lambda_1$ coincides with the $6^{\text{th}}$ dark band with wavelength $\lambda_2$,then the ratio $(\lambda_1 / \lambda_2)$ is:

What is the shape of the interference fringes formed on the screen due to a point source $P$,in the case shown here?

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

The colours observed in thin soap bubbles are due to

Assertion: Newton's rings are formed in the reflected system when the space between the lens and the glass plate is filled with a liquid of refractive index greater than that of glass; the central spot of the pattern is bright.
Reason: This is because the reflection in these cases will be from a denser to rarer medium and the two interfering rays are reflected under similar conditions.