A monochromatic light beam of waveleng
ttb7 ;,x r0j1urj3o7nl ey+4pb6ncx x7uazy :th λ is diffracted at a single slit of width
y lje7;x+n7y3p0ro 7bbut6:jcxt ,a z14nxur $b$. 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 $w$?