A monochromatic light beam of wavelength λ is diffr
ny3 nad 3zx6gb4- y32y hxl/tsacted at a single slit of width
3nbn-3gyhtdy2a4x6 x z3lsy/ $b$. 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 $w$?