A monochromatic light beam of wavelength λ
/pj2i,onaoa; is diffracted at a single slit of width
,inp /2oaa;j o $b$. 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 $w$?