Diffraction of waves through a narrow gap

Steps:

• Identify the phenomenon: Water waves encountering a small gap undergo diffraction, bending and spreading.
• Recall wave behavior: When the gap width is comparable to or smaller than the wavelength, waves emerge as circular wavefronts.
• Compare diagrams: Select the one showing waves radiating outward in all directions after the gap.
• Confirm: This matches Huygens' principle, where each point on the wavefront acts as a new source.

Why A is correct:

• A depicts circular waves spreading from the gap, illustrating diffraction as defined by Huygens' principle for obstacles smaller than the wavelength.

Why the others are wrong:

• B shows reflected waves bouncing back, not diffraction.
• C illustrates refracted waves bending due to speed change, irrelevant here.
• D displays straight-line propagation, ignoring the gap's diffractive effect.

Final answer: A