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

Explanation

(i) Fringe width of interference fringes is given by `beta = (D lamda)/(d) prop 1/d` . When d is infinitely small, fringe width `beta` will be too large. (ii) In such a case even a single fringe may occupy the whole field of view. Hence, the interference pattern cannot be detected.