In the interference pattern,energy is

The phenomenon of interference is observed in .........

Write the condition for constructive interference in terms of path and phase difference.

Consider the following statements about interference of light:
$A$. The interference fringes are equally bright and equally spaced.
$B$. At the centre of a bright fringe,the intensity is four times the intensity of the incident wave.
$C$. For constructive interference of two waves,the crest of one wave coincides with the trough of another wave.
Which of the above statements are correct?

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

Two coherent monochromatic beams of intensities $I$ and $4I$ respectively are superposed. The maximum and minimum intensities in the resulting pattern are