Diffraction depends on gap width relative to wavelength

Steps:

• Diffraction occurs when waves pass through a gap comparable to their wavelength λ.
• The extent of diffraction is governed by the ratio of gap width w to λ.
• Initially, the ratio is w/λ for the observed diffraction.
• With wavelength doubled to 2λ, new gap width w' must satisfy w'/2λ = w/λ, so w' = 2w.

Why C is correct:

• Similar diffraction requires the same w/λ ratio, per the wave diffraction principle; doubling λ thus doubles w to 2w.

Why the others are wrong:

• A: 0.5w halves the ratio, increasing diffraction beyond the original.
• B: w keeps the ratio halved, reducing diffraction.
• D: 4w quadruples the ratio, minimizing diffraction.

Final answer: C