In a diffraction experiment using a single slit, the angular width of central maximum decreases when:

In a single-slit diffraction experiment, the central maximum is the bright fringe at the center of the diffraction pattern. The angular width of this central maximum is defined as the angle between the first minima on either side of the central peak, and it is given by: Angular width = 2θ = 2λ / a,
where:

• λ is the wavelength of the light used
• a is the width of the slit

From this equation, we observe that the angular width:

• Increases when the wavelength (λ) increases
• Decreases when the slit width (a) increases

Therefore, when the slit width increases, the angle θ becomes smaller, and thus the central maximum becomes narrower — meaning the angular width decreases.