A monochromatic light beam of
mgterz,b2 je 11w(z. a wavelength λ is diffracted at a single slit of wid
tz r(. 2 ebmje1,wa1gzth $b$. 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 $w$?