question_answer

No interference pattern is detected when two coherent sources are infinitely close to one another. Why?

Answer:

                Fringe width, \[\beta =\frac{\lambda D}{d}\] i.e., \[\beta \propto \frac{1}{d},\] when \[d\to 0,\beta \to \infty \]. Fringe width is very large. Even a single fringe occupy the entire screen. The interference pattern cannot be observed.