Statement - I :For interference fringes to be seen, the condition$\frac{S}{S}<\frac{\lambda }{d}$should be satisfied. Where ‘s’ be the size of source slit, S is its distance from plane of two slits and ‘d’ is the distance between two slits.
Statement - II :In Y.D.S.E, if distance of source slit from the two slits (s) decreases, the interference pattern gets more sharp.

(a) If s is size of the source and S is distant of source from the plane of the two slits, then for interference fringes to seen, the condition is $\frac{\mathrm{s}}{\mathrm{S}}<\frac{\mathrm{\lambda }}{\mathrm{d}}$
As source slit is brought closer to double slit plane, S decreases, the  interference pattern gets less and less sharp. When the source is too close, the fringe separation remains fixed.
(b) As width of source slit is increased, the interference pattern gets less and less sharp. When the source slit is so wide that condition  $\frac{\mathrm{s}}{\mathrm{S}}<\frac{\mathrm{\lambda }}{\mathrm{d}}$
is violated, the interference pattern disappears.