Diffraction maximizes when wavelength nears gap width

Steps:

• Diffraction of waves is significant when wavelength λ is comparable to or larger than gap width d; initially, λ = d/5, so minimal diffraction.
• To increase diffraction, increase the λ/d ratio by enlarging λ relative to d.
• Halving frequency f doubles λ (since wave speed v = fλ is constant on water, λ = v/f).
• This changes λ/d from 1/5 to 2/5, making waves bend more around the barrier.

Why C is correct:

• Halving f doubles λ via v = fλ, raising λ/d and enhancing diffraction per Huygens' principle.

Why the others are wrong:

• A: Amplitude affects wave energy but not diffraction pattern or angle.
• B: Doubles d to 2d, halving λ/d to 1/10, reducing diffraction.
• D: Halves λ to λ/2, doubling λ/d inverse to 1/10, reducing diffraction.

Final answer: C