A monochromatic light beam of wavelen
l6m vz7kqz .+sgth λ is diffracted at a single slit of widt
l.6qkszzvm7+h $b$. 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 $w$?