Diffraction improves when wavelength matches gap size

Steps:

• Recall diffraction: bending of waves around obstacles or through gaps, most noticeable when wavelength is comparable to or larger than gap width.
• Assess current setup: some diffraction observed, so wavelength is somewhat comparable to gap.
• Evaluate changes: identify which increases diffraction effect by making waves bend more noticeably.
• Select option: increasing wavelength enhances spreading without altering gap.

Why C is correct:

• Diffraction is maximized when λ ≥ gap width (from Huygens' principle, where secondary wavelets spread more relative to obstacle size).

Why the others are wrong:

• A: Amplitude affects wave height, not bending pattern.
• B: Higher frequency shortens wavelength (λ = v/f), reducing diffraction.
• D: Wider gap allows straighter passage, minimizing bending.

Final answer: C