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. The intensity ratio of two sources is $1:4$. For this interference pattern,if the value of $\frac{I_{\max} + I_{\min}}{I_{\max} - I_{\min}}$ is equal to $\frac{2\alpha + 1}{\beta + 3}$,then the value of $\frac{\alpha}{\beta}$ will be:

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

Interference fringes are produced on the screen by using two light sources of intensities $I$ and $9I$. The phase difference between the beams is $\pi / 2$ at point $P$ and $\pi$ at point $Q$ on the screen. The difference between the resultant intensities at points $P$ and $Q$ is $(\cos 90^{\circ}=0, \cos 180^{\circ}=-1)$. (in $I$)

The ratio of intensities of two waves producing interference is $9: 4$. The ratio of the resultant maximum and minimum intensities will be:

Path difference between two light waves at a point $P$ for constructive interference will be