A monochromatic light beam of wavelength λ is diffracte
:qd oov3.e:rfke16 nd:zaw 0o d at a single slit of width
eaqv:1 oo:d 6no0fedk:w3 .rz$b$. 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 $w$?