Wave Diffraction Through a Gap

Steps:

• Waves diffract when passing through a gap comparable to their wavelength, causing spreading.
• For a gap equal to the wavelength, significant diffraction occurs as the gap size allows bending around edges.
• Diffraction alters the wave's path but does not change its intrinsic properties like wavelength.
• Wavelength remains constant, determined by the wave source and medium, not the obstacle.

Why A is correct:

• Huygens' principle states that every point on a wavefront acts as a source of secondary waves; with gap = wavelength, these interfere to produce diffraction without altering wavelength.

Why the others are wrong:

• B: Wavelength does not decrease; diffraction spreads waves but preserves wavelength.
• C: Diffraction does occur for gap = wavelength; no decrease in wavelength.
• D: Diffraction is present; waves do not propagate straight without spreading.

Final answer: A