The colour of light is characterised by which of the following characteristics?

Resultant intensity at the centre of the screen due to two coherent sources is $I_0$. If the sources are incoherent,then the intensity at the same point will be

Two monochromatic light beams have intensities in the ratio $1 : 9$. An interference pattern is obtained by these beams. The ratio of the intensities of maximum to minimum is (in $: 1$)

An interference pattern is observed at $P$ due to the superimposition of two rays coming from a source $S$ as shown in the figure. The value of $l$ for which maxima is obtained at $P$ is: ($R$ is a perfectly reflecting surface)

The optical path difference between two identical light waves arriving at a point is $31.5 \lambda$,where $\lambda$ is the wavelength of light used. The point is [Given: Two light sources are coherent]

Two identical light waves, propagating in the same direction, have a phase difference $\delta$. After they superpose, the intensity of the resulting wave will be proportional to