In the adjacent diagram,$CP$ represents a wavefront and $AO$ & $BP$ are the corresponding two rays. Find the condition on $\theta$ for constructive interference at $P$ between the ray $BP$ and the reflected ray $OP$.

Two coherent monochromatic light beams of intensities $I$ and $4I$ are superposed. The maximum and minimum possible intensities in the resulting beam are

Two identical light waves having phase difference $\phi$ propagate in the same direction. When they superpose,the intensity of the resultant wave is proportional to:

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).

The light beams of intensities in the ratio of $9: 1$ are allowed to interfere. What will be the ratio of the intensities of maxima and minima?

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: The phase difference of two light waves changes if they travel through different media having the same thickness,but different indices of refraction.
Reason $R$: The wavelengths of waves are different in different media.
In the light of the above statements,choose the most appropriate answer from the options given below.