A monochromatic light beam of
q4g id:t ;8b2ieyq,1 j ia2iglwavelength λ is diffracted at a single slit of wid
delib i; 2iagq:itg4q 218,yjth $b$. 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 $w$?