A monochromatic light beam of wavelength
l akcc(;ca 1 zn((+;(;zw;rysd gxcuhλ is diffracted at a single slit of widt
hcdk1a;y ((s(nag; zx;cu+l wrzc ; (ch $b$. 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 $w$?