If the wavelength of light is $4000 \, Å$, then the number of waves in a length of $1 \, mm$ will be:

Two coherent sources of light interfere and produce a fringe pattern on a screen. For the central maximum,the phase difference between the two waves will be,

In an interference experiment,the phase difference for points where the intensity is minimum is $(n=1, 2, 3, \ldots)$

The contrast in the fringes in an interference pattern depends on

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]

The frequency of a light ray having a wavelength of $3000 \ \mathring A$ is