A monochromatic light beam of wav
j/ 0, a(hgau0no+u grcelength λ is diffracted at a single slit of widt
,0ju/gagh aco+rn 0 u(h $b$. After passing the slit, a diffraction pattern is observed on a screen a large distance away. The width of the central maximum is $w$.
The screen is moved closer to the slit. Which of the following changes, done separately, could result in no change in $w$?