If the wavelength of light is $4000 \mathring A$,then the number of waves in $1 \ mm$ length will be

Two light waves of same intensity superpose at point $P$ with a phase difference of $\pi/3$. The resultant intensity at point $P$ will be?

Interference fringes are produced on a screen by using two light sources of intensities $I$ and $9I$. The phase difference between the beams is $\frac{\pi}{2}$ at the point $P$ and $\pi$ at the point $Q$ on the screen. The difference between the resultant intensities at point $P$ and $Q$ is (in $I$)

The intensities of two waves are $2$ and $3$ units,respectively. The average intensity of light in the interference region will be ......

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

Two independent monochromatic light sources produce waves given by $y_1 = 2 \sin \omega t$ and $y_2 = 3 \cos \omega t$. Which of the following statements is true?