A monochromatic light beam of wavelength λ is diffrac
z6x44.alknky,9t uea4 tbt1m ted at a single slit of width
,.yk zx4ltnk4bt4 6e1mu ta9a$b$. 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 $w$?