The phenomenon of interference is shown by

Two light waves having the same wavelength $\lambda$ in vacuum are in phase initially. Then the first wave travels a path $L_{1}$ through a medium of refractive index $n_{1}$ while the second wave travels a path of length $L_{2}$ through a medium of refractive index $n_{2}$. After this the phase difference between the two waves is:

Interference cannot be observed in two sodium lamps of equal power because the two waves do not have a .....

Two coherent light sources $A$ and $B$ are at a distance $3\lambda$ from each other (where $\lambda$ is the wavelength). Find the distances from $A$ on the $x$-axis at which constructive interference occurs.

In an interference experiment,the path difference between two interfering waves at a point $A$ on the screen is $\lambda/3$,where $\lambda$ is the wavelength of these waves,and at another point $B$ the path difference is $\lambda/6$. The ratio of intensities at points $A$ and $B$ is . . . . . . .

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