Two periodic waves of intensities $I_{1}$ and $I_{2}$ pass through a region at the same time in the same direction. The sum of the maximum and minimum intensities is

What is the path difference for destructive interference?

Two coherent plane light waves of equal amplitude make a small angle $\alpha (\alpha \ll 1)$ with each other. They fall almost normally on a screen. If $\lambda$ is the wavelength of the light waves,the fringe width $\Delta x$ of the interference pattern of the two sets of waves on the screen is:

The phenomenon of interference is shown by

The following figure shows sources $S_1$ and $S_2$ that emit light of wavelength $\lambda$ in all directions. The sources are exactly in phase and are separated by a distance equal to $1.5\lambda$. If we start at the indicated start point and travel along path $1$ and $2$,the interference produces a maxima all along:

Two sources are said to be coherent if they produce waves