A monochromatic light beam of
ivoo2ix g4. ul78qo2y wavelength λ is diffracted at a single slit of width
2lo8gix7 4oi qu2.vyo$b$. 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 $w$?