Question

Two monochromatic coherent point sources `S_(1)` and `S_(2)` are separated by a distance L. Each sources emits light of wavelength `lambda`, where `L gt gt lambda`. The line `S_(1) S_(2)` when extended meets a screen perpendicular to it at point A. Then
A. the interference fringe on the screen are straight lines shape
B. the interference fringes on the screen are strainght lines perpendicular to the line `S_(1) S_(2) A`
C. point A is an intensity maxima if `L = n lambda`
D. point A is always an intensity maxima for any separation L

Answer 1

Correct Answer - c
If the screen is prependicular to y-axis (line joinin the sources), i.e., xz plane, the fringes will be circular (i.e., concentric circles with their centers on the point of intersection of the screen with y-axis). In this situation, central fringe will be bright id `S_(1), S_(2) = n lambda` and dark if `S_(1) S_(2) = (2 n - 1) lambda // 2`. From all this, it is clear that shape of fringes depends on the nature of sources and direction of observation, i.e., position of screen