A monochromatic light beam of wavelength λ is diffracted at a
rgso za*zmsgbu :6 yr-8-l- z4single slit of width
z ur ggs-r8-zy aso*:lmb 64z-$b$. 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 $w$?