CBSE Class 12 · 2023 · Wave OpticsShort Answer

The fringe width is $\beta =\frac{\lambda D}{d}\propto \frac{1}{d}$.
(a) $\text{Sources infinitely close}$ ($d\to 0$): $\beta$ becomes extremely large, so a single fringe may fill the entire field of view and no distinct interference pattern can be detected.
(b) $\text{Sources far apart}$ ($d$ large): $\beta$ becomes extremely small, so the fringes crowd together and cannot be resolved as separate bright and dark bands.