$n$ incoherent sources, each emitting beams of intensity $I_0$, are superimposed at a point. The resultant intensity at the point is:

If the ratio of amplitudes of two interfering waves is $4: 3$,then the ratio of maximum and minimum intensity is

To observe a stationary interference pattern formed by two light waves,it is not necessary that they must have :

Two coherent sources $S_1$ and $S_2$ and a screen are arranged as shown in the figure. If the distance between the two coherent sources is $n \lambda$ and the distance of the screen from the nearer coherent source $S_2$ is $D$,then the distance of the first bright fringe on the screen from the point $O$ is (where $\lambda$ is the wavelength of the light emitted by the coherent sources).

Two light waves of intensities $I_1$ and $I_2$ having the same frequency pass through the same medium at a time in the same direction and interfere. The sum of the minimum and maximum intensities is

Two coherent monochromatic light beams of intensities $4 I$ and $9I$ are superimposed. The difference between the maximum and minimum intensities in the resulting interference pattern is $xI$. The value of $x$ is . . . . . . .