A monochromatic light beam of wavelength λ is
v 2k-/l9t zn5ev eylh0 diffracted at a single slit of width
et29k 0veyh-v l5nzl/ $b$. 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 $w$?