A monochromatic light beam of wavelength λ is diffract
c,s/asvpw ( l+hoq ,(ved at a single slit of width
(,hv, as cw(/+oqpl sv $b$. 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 $w$?