A monochromatic light beam of wavelength λ i
9+)*6bfacub so 1wycms diffracted at a single slit of width
bc*cm1 y6)s+fb owau9 $b$. 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 $w$?