Diffraction angle minimized by shorter wavelength relative to slit width

Steps:

• Recall single-slit diffraction: angular spread θ ≈ λ / a, where λ is wavelength and a is slit width; smaller θ reduces diffraction.
• Note slit width a > λ, so diffraction occurs but is limited.
• To decrease diffraction, reduce θ by decreasing λ (since a is fixed unless changed).
• Relate wave properties: λ = c / f, where c is speed of light and f is frequency; T = 1 / f, so decreasing T increases f and decreases λ.

Why B is correct:

• Decreasing time period T increases frequency f (T = 1/f), which decreases λ (λ = c/f), reducing θ per diffraction formula.

Why the others are wrong:

• A: Decreasing frequency f increases λ (λ = c/f), increasing θ and diffraction.
• C: Decreasing slit width a increases θ (θ ≈ λ/a), increasing diffraction.
• D: Increasing λ directly increases θ (θ ≈ λ/a), increasing diffraction.

Final answer: B