A monochromatic light beam of wavelength λ is diffra
alva ,nt-z y4hv k96.sfst; :gu.;otelz .v 9zcted at a single slit of width
;v l,ga vh9k.9yaz u:vs;l-6 z te.ott zfns4. $b$. 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 $w$?